Vapor Barrier Liners: Theory & Application

This article is reprinted here with permission from Backpacking Light Magazine.

Introduction

Occasionally during the FAQ portion of my slideshows, and frequently at the start of every winter, I receive questions about vapor barrier liners (VBL’s). The content and tone of these questions suggest a general misunderstanding of and slight mystery about them, so in this article I’ll attempt to offer a comprehensive review of VBL’s based on my understanding of and experience with them – basically, what they are, how they work, and when to use them.

I believe that VBL’s can be a critical and pivotal component of winter clothing and equipment systems—and, to a lesser degree, shoulder-season systems. Unfortunately, there is not much information available on VBL’s—an internet search returns information that is mostly outdated, incoherent rambling, or mistaken. My hope is that this article will result in (1) a greater understanding of VBL’s and (2) increased use of VBL’s by those who recreate outdoors in winter conditions, especially those who go on extended multi-day endeavors. This includes backpackers, snowshoers, skiers (Nordic, backcountry, and alpine), alpinists, ice climbers, mountaineers, and even ice fisherman and hunters.

What are vapor barrier liners?

A VBL is a non-breathable material that does not permit the transmission of moisture through it. They are typically made of fabrics like silicone-impregnated nylon, polyurethane-coated nylon, or Mylar; and there are at least two multi-layer proprietary fabrics too. In a pinch a VBL could be made from a plastic trash bag or a foil balloon—I have done both; in essence, any material that does not “breathe” will work. VBL’s are available as articles of clothing—including socks, gloves, pants, jackets/shirts, and vests—and as sleeping bag liners. Later in this article I will address the pros and cons of the various VBL fabrics and forms.

To avoid any question, it should be noted that VBL fabrics are fundamentally different than waterproof-breathable fabrics or treated-breathable fabrics (e.g. acylic-coated nylon, or any fabric with a durable water repellent finish). It is fair to question how “breathable” such fabrics really are, but even the poorest performing will still have some degree of breathability, whereas VBL’s do not permit any transmission of moisture, i.e. zero breathability.

Commercial Availability

No major outdoor manufacturers—not even technical mountaineering companies like Mountain Hardwear or Arc’teryx, whose core customers could arguably benefit most—offer VBL products. There are just a few mom-and-pop cottage manufacturers: RBH Designs has the most “extensive” product line; and other manufacturers like Stephenson’s Warmlite, Integral Designs, Forty Below, and Western Mountaineering also have a limited assortment of VBL products.

The limited commercial availability of VBL’s, I believe, is a function of two factors. First, VBL’s are optimal for just a narrow range of conditions—namely, multi-day outings in frigid temperatures—and so the potential customer base is very small. After all, how many people do you know who go on winter trips for a week or longer? And second, the defining characteristic of VBL’s—their lack of breathability—completely contradicts what consumers are regularly told they want in outdoor performance equipment—breathability—and thus the lack of intuitiveness keeps organic demand low.

I believe that there are a few excellent lightweight VBL products—most notably the Backpacking Light FeatherLite Vapor Mitts (manufactured by RBH Designs) and the RBH Designs Bonded VaprThrm Liner Socks—but that overall consumers are vastly underserved. In fact, I resorted to making my own VBL pants, jacket, and balaclava because I was not satisfied with what is commercially available.

A case study: Why I began using VBL’s

In the winter of 2004-05 I snowshoed 1,400 miles of the North Country Trail through both peninsulas of Michigan, northern Wisconsin, and northern Minnesota as part of my 7,800-mile 11-month Sea-to-Sea Route trek. With temperatures as low as -20 F and a consistent snowpack of 2-4 feet, this was unequivocally the most difficult part of the entire hike. It was my first serious winter experience, and a problem that became immediately clear was that my clothing and sleeping system failed to adequately manage perspiration. For example, my sleeping bag (a top-of-the-line model rated to -5 F with premium 850-fill down) would become more damp—and less lofty—with each long night curled up in it. My running shoes and Forty Below Light Energy overboots were frozen stiff each morning due to trapped foot-sweat from the days before. And sometimes I would perspire so much at night—without noticing it—that my clothes would steam when I emerged from my sleeping bag in the morning.

If not for being invited inside 1-2 times a week by generous locals and having the opportunity to dry my things, I definitely would have shivered through more nights than I actually did. The complete compromising of some of my most critical equipment was unstoppable with the system that I had.

Fast forward two years to January 2007, when I decided to revisit northern Minnesota in the depth of winter, but this time better equipped. Among the objectives of my 380-mile 16-day “Ultralight in the Nation’s Icebox” hike was to perfect my deep-winter gear list, or at least approach perfection. That meant bringing a VBL jacket, pants, socks, gloves, and balaclava. I intended to complete the entire trip without a night indoors, or at least feel that I was capable of doing so. (As it happened, I spent one night inside, about 5 days into the trip, with one of my favorite trail stewards, Ken Oelkers of Silver Bay.) After the trip I made a few small adjustments to my winter clothing and sleep system, but generally these systems were spot-on—they led to a tremendous improvement over my Sea-to-Sea experience.

Having realized the value of VBL’s, I also began experimenting with them in other situations, including during the shoulder seasons and on done-in-day skiing and snowshoe trips. In February and March 2008 I even used VBL’s while removing ice dams off of rooftops in Frisco, CO, including some windswept 7-story buildings at Copper Mountain.

In sum, I have become convinced of the value of VBL’s and have attempted to find the limits of their applicability. They are definitely most critical on multi-day trips in frigid conditions, but they are valuable for both shorter and warmer trips too.

Effects and Benefits

The principal effect of a VBL is stopping the transmission of insensible and sensible perspiration, i.e. sweat, away from your body, effectively creating a microclimate between the VBL and your body. (Without a VBL, perspiration would move away from your body and through outer layers (if applicable), and then hopefully evaporate into the atmosphere.) This entrapment of moisture has three benefits:

First, perspiration will not reach outer layers like a windshirt, insulated parka, or sleeping bag. This is hugely important because in cold conditions your perspiration will often stay in these layers: the dew point is somewhere between your body and the outside atmosphere, and your perspiration will condense from water vapor into actual water, thus wetting the layers. This will cause down and synthetic insulations to ultimately collapse. And it will cause unwanted evaporative heat loss with other fibers like polyester, nylon, and wool.

Second, the wearer is always keenly aware of their rate of perspiration, and they are better able to thermoregulate properly as a result. Without a VBL, you might begin to overheat and sweat profusely without fully realizing it. This will soak layers and cause dehydration, which will lead to poorer circulation and lower respiratory efficiency; you may also waste more time and fuel melting snow to get water. With a VBL, however, this scenario is far less likely to happen: you will notice the rainforest-like humidity level in the microclimate—or, if you really overdo it, the sweat dripping down your back—and you will react by removing layers or increasing ventilation.

Finally, evaporative heat loss is minimized. All forms of heat loss should be carefully managed in cold conditions, and a VBL is an effective way in which to manage evaporative heat loss. (The other types of heat loss are conduction, convective, and radiation.) To illustrate this point, imagine how it feels to work up a sweat while snowshoeing up a mountain and then resting for a few minutes at the cold, windswept summit. Brr…

Applicability: When to use VBL’s

There are no set rules, just guidelines, about when you might consider using VBL’s. In deciding whether to use VBL’s, and which exact items to use, I consider four factors:

1. RealFeel Temperature®. I do not necessarily use AccuWeather’s patented index, but I think the idea is useful—it is a measure of all of the environmental factors that affect how warm or cold I am. This would include ambient air temperature, wind, sun exposure, precipitation, humidity, and ground cover. I find that I can begin to wear VBL gloves in temperatures below 40 degrees F, a jacket and socks below 20, and pants below 10. If it is windy and/or cloudy, if precipitation is falling (particularly cold rain, sleet, or wet snow), and/or if I am walking on or through snow or ice, then I may be comfortable wearing VBL’s in warmer temperatures. If the conditions are opposite (no wind, lots of sunshine, no precip, and dirt or grass ground-cover), then it may have to be colder before VBL’s can be worn comfortably.

The maximum temperature at which a sleeping bag liner can be used is very dependent on the warmth of the sleeping bag. A liner will add about 5-10 degrees of warmth to a bag (not including the warmth preserved by preventing loft loss).

2. Trip length. The longer the trip, the more critical VBL’s become in maintaining the integrity of my clothing and sleep system. On a weekend trip, for example, loft loss will not be significant. On a week-long trip (or longer), however, the loss of a few degrees of warmth each night—due to perspiration entering the sleeping bag and wetting the insulation—would be much more noticeable and consequential. Without VBL’s, I would either need to dry my things during the day or bring an excessively warm sleeping bag so that by the end of the trip it would still offer enough warmth.

While the use of VBL’s is most critical during long-term endeavors, they can still be very valuable during shorter efforts. For example, towards the end of a full day of alpine skiing, when the sun disappears and the temperatures begin to drop, many skiers feel chilled because their boot liners, gloves, and clothing have become damp with sweat during the day. By wearing VBL layers skiers could avoid the compromising of their insulation and the sucking of heat away from their bodies by this trapped moisture, allowing them to catch one more lift at 4pm.

3. Type of insulation. Down is more susceptible to loft-loss than synthetics when exposed to moisture. Synthetics are still vulnerable in the long-term too, but the rate of degradation is less. Therefore, it is possible that I can stretch an all-synthetic system a few days longer than I could an all-down system. Ultimately, the all-synthetic system will fail too, but perhaps not before I finish the trip. Since down is significantly superior in its thermal efficiency, it’s debatable whether the all-synthetic system would be lighter—for example, I could put together a lighter weight all-down system that is unnecessarily warm at the start but that would still be adequate by the end.

4. Effort intensity. In order to avoid over-sweating while using VBL’s, I must be attentive to body heat generation and be willing to regulate it. This is fairly easy during steady, low aerobic activities like hiking, snowshoeing, mountaineering, ski touring, snowmobiling, ice fishing, etc. The task becomes more difficult for activities like alpine skiing and climbing, when periods of intense exercise are followed by periods of sedation, e.g. leading a pitch and then belaying a climbing partner up to the anchor. For high aerobic activities like running, skate skiing, or alpine touring (AT) racing, I find it almost impossible to avoid sweating and therefore VBL’s are probably inappropriate in this context.

Developing your own VBL system: Insider’s Tips

By this point in the article you hopefully understand what VBL’s are, and why and when you should use them. In this final section I hope to explain how to integrate them into your clothing and/or sleeping system, and to point out the pros and cons of various VBL fabrics and forms. All VBL’s are not created equal, and I have developed preferences for what I think is my optimal VBL system.

Layering. VBL’s are typically worn directly against the skin or with a base layer between the VBL and the skin. Personally, I prefer the latter approach, which I believe has a few key benefits. First, the base layer creates a small buffer that minimizes discomfort (i.e. “clamminess”) but without reducing sensitivity to perspiration, which I need in order to make informed thermoregulation decisions. Second, by wearing a base layer I protect my skin from direct contact with the frigid air, which would happen otherwise if I needed to ventilate my “next to skin” garment by unzipping it. Finally, the base layer seems to keep my skin dry enough that moisture-related skin issues (e.g. maceration)do not arise. I like to pair VBL’s with lightweight, form-fitting polyester base layers (like those made by CW-X), not wool. Polyester can be knitted thinner and does not absorb moisture like wool does, which may result in decreased sensitivity.

Forms. An effective VBL system needs to consist of either a sleeping bag liner or a full multi-piece VBL clothing suit. It is redundant and unnecessary to use both a VBL liner and a VBL suit. Personally, I prefer to wear VBL clothing, which has a few advantages. First, I can use a lighter sleeping bag because I can sleep with all of my clothes on—a base layer between my skin and VBL, then all of my other layers outside the VBL. With a VBL liner I can only sleep in my base layer garments; otherwise all of my layers would get wet. Second, I already have all of my clothes on in the morning when I wake up, which saves time and body warmth. Even if I brought all of my non-base layer clothes into my sleeping bag but outside of a VBL liner, I will lose a lot of heat when I try to change into them. And third, I keep all of my clothing dry at night and during the day, except for my base layers, which may become slightly moist with perspiration. If I were to rely exclusively on a VBL bag liner, perspiration would enter and become trapped in my insulated jacket and pants while I wear them during rest stops or in camp. The one downfall with VBL clothing is that I need to have a complete VBL suit, which is heavier and more complex than a bag liner. In the long term, my sleeping bag could be compromised if I am not completely covered with VBL’s. A complete suit would include socks, pants, jacket, gloves, and a hat or balaclava.

Fabrics. The ideal VBL fabric would be a non-slip, 1-layer, 4-way-stretch ultralight fabric with a good hand. To my knowledge this fabric does not exist. Until it does, we have sub-optimal options. Silicone-impregnated nylon and reflective nylon (e.g. Mylar) is slippery, crinkly, and noisy. RBH Designs’ VaprThrm® fabric is three layers and designed to be worn “next to skin”; it feels like a softshell fabric, minus the breathability. This fabric is heavy, and it offers less adjustability than a 3-piece system consisting of a thin base layer, VBL shirt, and an outer layer like a windshirt or ultralight insulated parka. Without stretch, these fabrics are impractical for pants because they are so constricting. The only option is to make baggy pants, which are not conducive to creating a small microclimate next to the skin.

Features. It is very uncomfortable to sweat while wearing VBL’s and so I am constantly trying to regulate my body temperature to avoid it. Regulating can be done quickly and efficiently via features like zippers (e.g. front chest, abdomen, pit, arm, and full leg zips), removable parts (e.g. arm sleeves), and easy on-off adjustments like integrated hoods or mitt idiot cords. During periods of rapid warming or cooling, like during or just after a rest stop, these micro adjustments may be inadequate and entire layers may have to be added or removed.

Conclusion

Vapor barrier liners can be a pivotal and critical addition to wintertime and shoulder-season clothing and equipment systems, especially for those who are outdoors for long periods of time in frigid conditions. VBL’s prevent loft-loss, encourage better thermoregulation, and minimize evaporative heat loss. There seems to be a good deal of confusion and mystery about VBL’s, and through this article I hope that I managed to improve general understanding and inspire more widespread use by explaining what they are, how they work, and when and how to use them.

Vapor Barrier Liner Slideshow: the technology put to use


My first winter experience was during my 7,800-mile Sea-to-Sea hike, during which I snowshoed 1,400 miles through Michigan, Wisconsin, and northern Minnesota (pictured) in the first three months of 2005. It became immediately obvious that my sleeping and clothing system, which was simply a warmer version of a conventional lightweight setup, failed to adequately manage perspiration and loft-loss.


I returned to Minnesota in January 2007 in order to perfect my winter system, which included a complete VBL suit: jacket, pants, socks, gloves, and balaclava. The system was an enormous improvement over the Sea-to-Sea experience – the VBL system eliminated loft-loss, improved thermoregulation, and minimized evaporative heat loss. Notice the accessory carabiner on my shoulder strap, which is one of the ways I make fast and efficient adjustments to my layering system.


During my Ultralight in the Nation’s Icebox hike, I was joined for a night by Backpacking Light staffer Sam Haraldson, whose clothing and equipment system lacked VBL. After hiking for several hours, Sam removed his waterproof-breathable jacket to discover a layer of frost inside it, due to his perspiration turning from vapor into water as it reached the dew point, which was inside his clothing system. If he had been out for more than a night, the moisture inside of his system would have caused his insulated jacket to fail.


Without a VBL, it is necessary to dry clothing and equipment frequently. This is difficult in cold conditions, but possible. Even though I had VBL, I took advantage of a relatively warm and sunny day to dry two sleeping bags and a bivy sack, which had become slightly damp due to snow-covered ground and frozen moisture from breathing.


VBL are most critical on long-term trips in frigid conditions. But I have also found them useful during the shoulder seasons and done-in-a-day winter efforts. My favorite example of the latter is when I used them while removing ice dams off rooftops in Frisco, CO – the VBL helped to minimize evaporative heat loss and kept my insulation dry, which prevented me from getting chilled by the end of the day.


Steady, low-aerobic activities like hiking, snowshoeing, mountaineering, and ski touring are most conducive to the use of VBL because your heat output is consistent and can be managed easily. Stop-and-go activities like climbing and backcountry alpine skiing are challenging for VBL use because your heat output is more erratic.

87 Responses to Vapor Barrier Liners: Theory & Application

  1. Michael March 17, 2012 at 9:47 am #

    I say to each his own. However, I only use breathable water proof or water resistant laminate fabrics with varying thickness levels of polyester fleece and taped or non taped seams. (depending on weather, temp, wind etc) I spend most of my time skinning, bootpacking at high altitudes and extreme weather. I personally disagree with the use of VBLs. The micro-environment creates a pseudo 2nd skin that you can never remove without going indoors (think literal sweatsuit). Moist micro-environments create fungus issues. Mold likes to grow in cool, damp places. Fungus breeds a whole derivative set of issues for the solo trip enthusiast. Hello VBL 2nd skin void. People think I’m crazy because my glove collection at times can be worth more than my car. Different gloves and mitts for different times during the day. This can be more difficult to manage on long treks. I live work, play year round at 10,300′ elevation. I spend well over 150 days a year from 11,000-14,000′ outdoors. Just my opinion. oh, and I make outdoor gear which is worn by the highest based Search and Rescue team in North America.Again, to each his own…

    • Andrew Skurka March 17, 2012 at 10:05 am #

      I have never had fungus problems with VBL’s. Wearing merino wool base layers and socks — as opposed to polyester, which isn’t naturally anti-microbial like wool fibers are — may help with this. I also don’t find that the system is as sweaty as most people would think — VBL layers only become a sweatsuit if you don’t ventilate and/or regulate your output.

      I’ll also point out that I don’t need to carry numerous glove systems and that my clothing system is versatile across a very wide range of conditions. The VBL layers are a cornerstone for this system.

  2. John March 30, 2012 at 8:12 pm #

    What fabric did you use to make your own VBL? What sort of patterns did you use for the clothing?

    • Andrew Skurka March 31, 2012 at 3:54 pm #

      For a top, you can use any shelter fabric, e.g. sil-nylon, Cuben, PU-coated polyester or nylon.

      I haven’t found an ideal material for pants, because as far as I know there is no non-breathable fabric that stretches, and I really like my pants to stretch, since otherwise they restrict movement. My homemade VBL pants are made from sil-nylon.

      Re patterns, consider trying to replicate the dimensions of your favorite shell/raingear pants and bottoms.

      • Hrvoje April 28, 2012 at 9:53 am #

        Hello.
        I have ordered the AMK SOL Emergency Bivvy, just for emergencies, and now after stumbling onto your great site am contemplating on maybe using it, when needed, as a VBL liner.
        There is some videos and reviews on youtube of this ultra-light bivvy bag, and it just might be what you are looking for to put into pants to create a vapor barrier, since it looks just stretchy enough that it might work…
        Just a thought… Stay safe and enjoy the great outdoors…
        God bless.
        H.

        • Andrew Skurka April 28, 2012 at 10:01 am #

          Beware, justifying gear decisions on the grounds of “just in case” can be a slippery slope. Make sure the scenario you are concerned about is actually likely, and that the “solution” to this scenario is actually a solution.

          Will check out the product you referenced. Thanks for the tip.

      • Ed November 17, 2012 at 3:07 am #

        Perhaps you could look into PVC for pants material. It’s spandex covered in a layer of PVC. It’s not the most durable fabric, but given that it would be used just above your base layer it should be fine. I have a hoodie made out of it that I used as a raincoat for eight years (with proper care) before it started to wear out, and I can tell you that thing did not breath at all.

      • Dave M. June 30, 2014 at 11:27 pm #

        Have you considered using pleats and gussets to achieve freedom of motion in slim-cut pants? Gussets require extra seam length, which may not be desirable for vapor-tightness, but pleats seem like all win.

      • David October 13, 2014 at 3:32 pm #

        Just to potentially inspire some options: materials such as rubber, urethane, latex, and silicone can be air-tight and flexible. Very thin urethane films are amazingly resilient and puncture resistant, too. Perhaps a good VBL could be made with these flexible materials in some areas and traditional shelter fabrics in others?

  3. Steve April 8, 2012 at 6:43 am #

    Andrew,
    First, thanks for your time researching, experimenting, and publishing your findings. I am new to hiking, two years, and section hiking the AT. I seem to be gravitating to off-season hiking avoiding the crowds. I hiked the first weekend in March at around 1500′ in sleet and slept in a 30 degree down bag, REI Bivy, with my synthetic base layer and woke up 3:00 in the morning because I was damp and very cold. The bag was wet on the outside, my base layer was damp on my skin and inside of the bivy was slippery wet. Luckily, I was near a town and was able to make it to a laundromat and dry everything that morning. Last year, I hiked Vermont for a week in late August under wet conditions, feet were wet the whole time but was wearing wool socks and I never felt uncomfortable. Getting to the question now, :), it seems that wearing a thin wool base layer next to the skin would be more comfortable than synthetic next to the skin. I say this because, as soon as you climb out of the VBL\sleepbag, the cold air is going to hit your base layer and you will be immediately chilled but with wool’s inherent insulation properties while damp or wet, would reduce this effect. Also, based on your findings, if I had slept in a VBL that weekend, I assume the down bag or bivy inside would have been dry, correct? Thanks for your response and time Andrew.

    • Andrew Skurka April 8, 2012 at 10:13 am #

      To summarize your experience in March:

      * Polyester base layer
      * Down sleeping bag
      * Bivy made of waterproof/breathable fabric

      …combined with…

      * High humidity
      * Cold-ish temperatures
      * Sleet

      I would not recommend this system in general, regardless of the conditions. And for the conditions you experienced, this is a particularly bad setup. Here’s what happened:

      * The breathability of the bivy fabric is limited even under the best conditions. And in this case it was completely negated by the high ambient humidity — since it was very humid outside the bivy, there was no where for the moisture inside the bivy (from perspiration) to go, so it stayed trapped within.

      * The cold temperature put the dew point inside your sleep system, causing water vapor to turn into water liquid inside your system. For example, if it was 35 degrees outside your bivy and 80 degrees inside your sleeping bag, and if the dew point was 45 degrees, then the transition point between water vapor and water liquid would be somewhere inside your system.

      * Down absorbs ambient humidity, as well as water. In this case, it was getting wet from both. And wet down does not insulate very well.

      Having a merino wool base layer would have helped some in keeping you warm, but I think the conditions degraded your system so severely that you probably still would have been very cold and would have needed to head into town the following day.

      If you had a VBL bag liner or clothing, your sleeping bag would not have become wet from perspiration, which would have improved your situation. But the down still would have absorbed ambient humidity, causing loss of warmth.

      In the situation you described, my preferred setup would have been:

      * A-frame tarp, which offers great ventilation and ample working space underneath
      * Water-resistant bivy, which doesn’t have the breathability problems of the waterproof/breathable bivy
      * Synthetic-insulated quilt
      * Synthetic insulated parka and possibly pants
      * Merino wool base layers

      This system would not be immune from moisture problems but would be much more resistant to them. This is a fairly standard go-to setup for me when hiking in the cold and wet conditions you have described.

      • John March 22, 2014 at 4:39 am #

        A Warmlite bag would solve your sleeping bag issues.

  4. Evan Ravitz April 14, 2012 at 8:52 pm #

    I started using Stephenson Warmlite gear in about 1972. It’s the best for winter use. I’m about to turn 60 now, avoiding winter camping and only encountering “winter” high in the Rockies in summer when it snows occasionally. For me, vapor barrier is most useful for sleep when you are generating the least body heat and are protecting the most important insulation, your down sleeping bag.

    Mexico’s Copper Canyon, where I guide, is so deep that there are some orange and banana trees in the bottom -and occasional snow on top in winter. So I carry light clothing but risk coming up to meet a snowstorm. I wear sandals but carry plastic bags and heavy socks just in case, to avoid frostbite in the worst case scenario.

  5. James Jenden May 1, 2012 at 8:28 pm #

    Andrew, I’m pretty much at where I’m going to stay as far as gear goes, partially because I’m quite satisfied with what I have, and partially because I have no more money to spend on it. That said, if/when I have more money, I think I’ll take a look a VBLs. Seems like a good system. Sleeping with down has some compromises, and it sounds like the VBLs solve these.

    Not sure if you’ve tried out jackets from Buffalo Systems UK, but I think they’d be right up your alley. They use shelled micro pile to create that same kind of microclimate. Keeps you warm even if you’re soaking wet, and they don’t weigh that much. Hard to find in the states, but if you’ve ever used Marmot DriClime, that’s basically what they are, just at a higher level I guess. Windproof outer, and interior with minimum contact. Basically creates a wetsuit affect.

    Also, I’m sure you’ve heard of it before, but you should try a bivy made with NanoShield. It’s a really water resistant fabric that breathes a lot better than a rain jacket. I have a tent made with it, and I like it a lot. A windshell made with this would weigh very little, but be seriously useful.

    Thanks for being a gear nut. Makes me feel less weird.

    • Andrew Skurka May 1, 2012 at 11:07 pm #

      I am a gear nut only to the extent that being one keeps me safer and more comfortable during my trips. Geeking over gear in the interest of gear has never done much for me.

  6. Lance Hollars, Group One Equipment July 22, 2012 at 7:45 am #

    Many people are not that aware of their thermal regulating mechanisms. Use of a vapor barrier can increase that awareness and the experience gained and increased skill will help users stay safer and more comfortable. I am reminded of the plastic bags we put inside our snow boots as children.
    Being in the business I think of the concept, Breath-ability for comfort and resistance for warmth* It is all about that balance. There are new materials out now that give down a run for it’s money and mitigate moisture issues much better.

  7. Sotaro October 3, 2012 at 1:19 am #

    Hello,
    Long ago, when doing a 6 day spring ski expedition across the Sierra Nevada in Central California the group I was with was advised to use VBL. Being poor I used small plastic bags for my socks and larger plastic bags for my sleeping bags. It was warm during the day, so I only used the VBL at night, except for the socks. I wore a thin layer of polypro (this was 25 years ago) and put the plastic bag with holes for my head and arms on. If I thought I would be cold I would add another layer of fleece. Around my ankles I would position the other plastic bag. As I cooled off I would pull up the bag. The VBL made a big difference in warmth, at least 10 degrees F I think. It is also very light and very cheap. Our guide advised us to remove all layers of clothes once a day, so in the morning I would take the VBL off and change the underlayer. It is definitely the cheapest and lightest warmth you can get.

    On another topic, the night I ate a cube of butter was the warmest and most comfortable night I have snow camped!

  8. Mike Tunley November 18, 2012 at 5:42 pm #

    I’m a recent VBL convert. I’m using RBH socks and shirt extensively while winter biking where balancing ambient (20 to -20f), windchill (5-20 mph) and effort (sweat) can be tricky. My first experiences with the NTS shirt was I was getting very cold on my front, where the shirt was touching my skin. SoI used a fancy patigucci polypro with which I got too warm (read sweat). On a whim I tried a mesh shirt made by Wiggy’s and had outstanding results. The mesh helps establish a layer of dead air space between myself and the VBL without any conductive heat loss. It worked so well I paid nearly three times as much for a Brynje shirt from Norway. Even more outstanding. I believe the mesh is the missing element in VBL systems.

    • Andrew Skurka November 18, 2012 at 5:51 pm #

      I figured that mesh base layers would work really well underneath VBL’s, so it is good to know that they in fact do. One problem to expect, however: mesh is not worthy as a standalone base layer, since it does not offer protection against UV or wind. So if you expect that sometimes during your outing you may need to strip down to your base layer due to relatively warm temperatures, mesh may not be a good choice — more of a concern on longer trips than short ones.

    • Scott March 18, 2014 at 10:39 am #

      Hi Mike,

      I am also a winter cyclist and commuter. I live in Minnesota, so similar temps of 20F to -20F. I have been considering the same VBL setup for some time now; specifically, the RBH NTS shirt. My current setup – Westcomb hardshel (breathable, “waterproof”), mid-weight fleece, and light or midweight wool baselayer depending on temperature – works for me down to about -5F. Below that, things get pretty uncomfortable (largely because I’m still figuring out my facemaks setup).

      I would be very interested in hearing your specific experiences in this application. My main concern would be sweat regulation. Obviously you’re going to be a bit chilled at the start. But do you think it’s possible to show up to work without being drenched after a mild-paced 8mile commute?

      I am also interested in using it for more athletic, fat tire trail riding. But I don’t really care about being sweaty after those rides.

      Finally, do you ever use the NTS shirt causally? For instance, as an alternative for a mid-weight insulation layer?

      Thanks!

      P.S. – would be willing to take this side converstion in a P.M./email format if preferred

      • Andrew Skurka March 18, 2014 at 5:24 pm #

        For such a short effort and for such a relatively high aerobic activity, I don’t think that VBL layers make sense. I thankfully don’t have to commute to work, but I do run throughout the winter, and for really cold conditions like that I find that breathable but warm layers — like merino or fleece sweaters, and expedition-weight tights — work best, possibly combined with a wind-breaking layer if needed (probably in your case, not always in mine).

  9. Jim Zajac November 26, 2012 at 1:48 pm #

    If we are normally loosing moisture through our skin that is causing our gear to loose it’s insulating qualities and we stop that loss with a VPL where is that moisture going? It seems the quantities of moisture must be fairly large. Is the inner liner layer able to handle it all or will I end up will pools of sweat on my socks?

    • Andrew Skurka November 26, 2012 at 1:58 pm #

      The quantity of moisture is large over the long-term. Think about how much you perspire over the course of a week — now imagine if your clothes trapped all of that moisture.

      VBL’s make you more sensitive to your perspiration (because you’ll notice “pools” long before they happen) so you dial back your effort or peel off layers so you sweat less. Some of the moisture will collect in your base layers, which you can dry through ventilation, sunshine, or a quick fire. Other moisture may freeze to the inside of your VBL, and it can be simply dusted off.

  10. Ben December 2, 2012 at 12:10 am #

    You say: “Some of the moisture will collect in your base layers, which you can dry through ventilation, sunshine, or a quick fire. Other moisture may freeze to the inside of your VBL, and it can be simply dusted off.”

    If moisture that freezes in a baselayer can be dried through ventilation or sunshine, then why is it that moisture frozen in a insulating layer worn without a VBL system cannot also be dried through ventilation or sunshine? Wouldn’t the same drying methods used on a VBL baselayer also be effective for drying the damp/ frozen non-VBL insulating layer?

    • Andrew Skurka December 2, 2012 at 12:13 am #

      Insulated layers are thicker and more removed from body heat, this absorbing mote moisture and lacking an additional drying factor.

    • Jon Moran March 5, 2014 at 7:45 am #

      I think Ben twisted your statement around ….

      “If moisture that freezes in a baselayer can be dried through ventilation or sunshine, then why is it that moisture frozen in a insulating layer worn without a VBL system cannot also be dried through ventilation or sunshine?”

      Moisture doesn’t freeze in base layer – unless you are dead

      Base layers are designed to wick and dry quickly. Wet down is not designed to dry quickly – just the opposite. It takes forever to dry wet down.

      • Andrew Skurka March 5, 2014 at 8:51 am #

        Yes, wet down takes forever to dry. But without a VBL the down is just likely to get damp. Depending on daylight temperatures and solar strength, you may or may not be able to dry the insulation. I wouldn’t count on it on a trip in MN in January, but AK in April, that is more likely.

  11. jfjobin December 6, 2012 at 7:40 pm #

    Thanks for this article.

    questions:

    cuben fiber or silnylon for vapor barrier cloth MYOG?
    > Skurka: Both would work since they are both non-breathable.

    if cuben, .51 or .74 cuben?
    > Skurka: Given the anticipated level of abrasion, I would go with the heavier stuff.

    rutalocura raft river jacket a good option for VB jacket?
    > Skurka: It’d work, but personally I prefer a VBL shell that is more like a rain jacket (in terms of fit and material weight) than a windshirt.

    “waterproof “zipper or normal zipper,change something?
    > Skurka: If you want to fully embrace the VBL concept, then you’ll want a waterproof zipper. But given the minimal amount of moisture that passes through a zipper, I think you’d be okay with a standard zipper too.

    pit zip a good option for medium activity?
    > Skurka: Yes, a very good option. Ditto for arm vents. And a two-way zipper. There are many situations where you want some of the warmth and wind protection of a shell, but not all of it. If your VBL layers do not have good venting, you’ll hate them during these times.

    thanks
    J-F

    • Andrew Skurka December 6, 2012 at 9:47 pm #

      Replied in-line to your questions.

      • Monel December 31, 2012 at 12:32 am #

        VBL for a sleeping bag?

        Andrew, I’ve seen a couple mentions of a cuben fiber / down filled sleeping bag.

        The trip I’m preparing for is a Gates of the Arctic Traverse in August, you know the terrain & weather I’m sure. The cuben/down seems to me to be a great idea, very light, very warm, waterproof on both sides, reasonably comfortable.

        My problem is I’ve never liked sleeping in a sleeping bag with even a waterproof breathable shell because it feels noticeably clammy to me. I sleep much more comfortably in breathable nylon shelled bags. I don’t like sleeping in bivies for the same reason. I can feel the humidity build up and don’t like it. Thinking about it, I’ve experienced the same thing sleeping in a small car with the windows closed. Ugh.

        It also seems that one would need to carry a warmer (and heavier) waterproof down quilt in the first place being reduced to wearing only a thin base layer under the quilt.

        In other words, with a cuben/down quilt, I can’t quite see wearing my pertex / climashield apex insulating pants & anorak under my quilt for added warmth as I do now with a synthetic quilt.

        Your thoughts?

        p.s. I don’t track this sight so would appreciate it if you could copy me via email if you reply.

        Best regards,

        Monel

        • Andrew Skurka December 31, 2012 at 7:35 am #

          I much prefer VBL clothing over a sleeping bag liner:
          I can wear all my clothes to bed, not just a base layer, and
          I get out of my bag in the morning with all my warm clothes on, instead of having to put on cold clothes that sat outside my bag all night.

          Sleeping bags with marginally breathable shells (e.g. “waterproof-breathable”) or non-breathable shells (e.g. cuben fiber) are a bad idea. The former will cause a lot of moisture to get trapped inside the bag, thus wetting the insulation. The latter will make it very difficult to get moisture out if it ever manages to get in (e.g. through untaped seams, or directly through older fabric that has lost its waterproofness). This would be more of a concern in wet places. Another problem with this construction is that again you can only wear a base layer to bed.

  12. Clueless December 31, 2012 at 9:47 am #

    I spent 8 days in Yosemite recently with a down bag camping in the same spot each night, in 14-35 degree weather, with snow. My down did get compromised somewhat where the footbox accidentally touched the tent wall, and around areas where I was breathing. There was some loft lost too. I was somewhat concerned that compressing the bag to move to new location might clump the down in future long winter trips.

    Using a VBL inside the bag seems to be a good solution, but it got me thinking about something I’ve read elsewhere, that the use of synthetics inside a bag might bring the dew point into the insulation.

    I guess I never quite understood why that would be the case, is that adage suggesting that if one were to sleep in a bag with only baselayers on, that the temperature in the bag would be higher than if a person was wearing synthetic layers? What’s the significance of synthetics? Is there another mechanism at play here, and does the use of a VBL fall into that scenario too? (to a smaller degree of significance of course, since perspiration in the bag would be minimized.)

    • Andrew Skurka December 31, 2012 at 10:02 am #

      In those conditions — cold and snowy — for that length of time, I’m certain that your bag lost some of its loft, unless you took action to prevent this from happening, e.g. dry the bag in mid-day sunshine. The degradation would be more severe if it had been colder or wetter, or if you’d been out for longer.

      You must have read some incorrect information about synthetic versus down insulation with respect to dew points. The mechanics are the same for both types of insulations:

      Your core temperature should be about 98.6 degrees. The temperature of your skin is probably a little colder, say 90. By the time you move through your base layer and puffy jacket, the temperature is about 60. By the time you move through a winter-worthy sleeping bag to the bag’s external shell fabric, the temperature is 10 degrees. The dew point was probably between 60 and 10 degrees; the precise temperature is a function of ambient humidity — if the air is almost completely saturated with moisture already, the dew point will be higher. (To better understand dew point and humidity, visit Wikipedia.) As you sleep you perspire, insensibly. As this moisture moves away from your body towards the drier ambient air, it hits the dew point, converts from vapor into liquid, and wets your insulation.

  13. Greg S January 11, 2013 at 12:04 pm #

    So I’m starting my NOBO Appalachian Trail thru-hike around February 15th of this year. I have an ultralight REI 0 degree 800 fill down bag that has served me very well over the years. Ive gone winter camping with it many times in the Adirondack mountains of NY but nothing longer than a few days.
    Did you find VBL’s a welcomed necessity during your AT thru-hike?
    I see you prefer VBL clothing over a bag liner…is there a particular setup you recommend that might work best given my scenario?
    I anticipate encountering the wet/humid conditions typical to the southern appalachians and certainly I’ll be facing winter weather. Is it inevitable that my bag will become compromised without the use of VBL’s or do you think I’ll be okay with preventive sun drying?

    Thanks,
    Greg

    • Andrew Skurka January 11, 2013 at 12:08 pm #

      In general, temperatures on the southern AT in mid-February will not warrant VBL’s.

      • Greg S January 11, 2013 at 12:32 pm #

        Thanks for the advice. I had been reading some conflicting posts on whiteblaze, good to have an expert clear things up.

        I’ve also heard that VBL socks can help to prevent boots getting damp due to perspiration and can be especially helpful with leather boots, which retain moisture longer than synthetic. Is this true?

        I’m concerned about maintaining good foot health throughout my trek, and especially since I’m looking to keep an average pace of 25-30 miles per day I know my feet will be taking a beating.
        What techniques or gear have you found work best in keeping healthy feet?

        • Andrew Skurka January 11, 2013 at 12:52 pm #

          That’s the problem with whiteblaze and a lot of other community sites — too much misinformation and conflicting information, and a terrible signal to noise ratio.

          VBL socks can help prevent shoes from getting wet due to perspiration. This becomes a problem on cold mornings because your footwear will freeze. Not the end of the world, but highly uncomfortable. Yes, leather boots typically are more difficult to dry than those made of synthetic materials, though “waterproof” synthetic boots won’t be much better.

          If you don’t know how to take care of your feet (which is a book-worthy subject that I won’t even try to address in this comment) and if you’re asking about boots, I might advise you to be more conservative in your mileage goals. That clip is generally achievable only by experienced backpackers and endurance athletes who have figured out the gear and skills they need to move fast and efficiently.

          • Greg S January 11, 2013 at 2:02 pm #

            Is there a particular book on long-distance foot care you might recommend? I think I should have been a little more specific with my question, although you answered it for the most part. I’m trying to figure out any adverse effects long-term winter hiking might have (frozen boots namely), but given what you said it seems more like an issue of comfort rather than necessity.
            Perhaps 30 miles is a little ambitious, although in my 12+ years of hiking I’ve found the asolo TPS 520′s work well during my multi-week outings, especially in rugged terrain such as the Rockies. Did you find the terrain on the AT in the mid-Atlantic region demanding enough to require boots, or will my Salomon trail runners suffice?

          • Andrew Skurka January 11, 2013 at 2:04 pm #

            In the interest in keeping these comments related to the article, I’d ask you seek another article or resource on AT-specific footwear.

          • scott February 20, 2013 at 12:00 pm #

            On my last snowshoeing trip, I solved my frozen boots in the morning problem at temperatures around 20 degrees. I simply put some cheap pocket warmers inside my socks, stuffed them in the toes of my boots, then stuffed my mittens inside. 12 hours later, my boots were still warm.

          • Andrew Skurka February 20, 2013 at 12:04 pm #

            That’ll work at 20, but not at -20 or probably even 10, depending on whether you keep your shoes near your body at night.

      • Duncan Coolidge November 20, 2013 at 12:43 pm #

        Andrew,

        It is interesting to read the critics of the vapor barrier approach who have never actually experienced the remarkable performance at sub zero temperatures. In all it offers the benefit of preserving the insulating capacity of down by keeping it dry, and reducing the amount of insulation needed overall by preventing the cooling effect of insensible perspiration. Using a light layer of synthetic long underwear, then a light rain suit, followed by heavy fleece my summer weight down bad provided more than enough insulation to keep toasty warm at zero degrees. An impressive performance. For those people with cold extremities, feet and hands, even something as simple as a bread bag over a liner sock and then a heavier insulating sock will make your feet feel like they are being warmed by a wood stove. For your hands plastic disposable gloves will work, or alternatively exam gloves from the pharmacy will do the trick. There is no need to buy expensive gear to outfit yourself. In fact if you can find someone handy with a sewing machine a few yards of the lightest silnylon will serve to fabricate a rudimentary pair of pants and tunic top. In the final analysis that setup will weigh far less than a winter weight down bag and all the accumulated moisture of days out in the cold.

  14. Bobby Quick February 4, 2013 at 1:37 pm #

    Andrew,

    Great article and fabulous info! Thanks so much for getting it out there. I have been pushing into the winter camping more and more and have found incredible benefit to using a VBL. I have only experimented with clothing VBL’s while hunting and have found that I really have to be careful and regulate myself as you have mentioned.

    Recently, I purchased a sleeping bag VBL made by Western Mountaineering and LOVE IT! I have tested it out in a 32 degree WM Summerlite bag in -9 degree weather… Here is the link to my videos if you care to take a look. My sleep system weighs in at less than 3 lbs and I have slept under the stars in below zero weather with no problems. All thanks to a VBL!!!

    Sleep system test: http://youtu.be/lcJI_puPHfc

    Follow up video: http://youtu.be/ZZ349q3qsAA

    Actual field use: http://youtu.be/-oAJPhJbl-g

    Sorry for all of the links, just super excited to share about a product that perfoms when applied correctly! Thanks again for all that you do!

    Bobby Quick
    Armchair Outdoors

  15. Greg Borchert April 1, 2013 at 9:07 am #

    Thank you very much for an informative article. I could find no relevant information on VBL usage anywhere, so truly appreciate you sharing your knowledge in this area with the rest of the world.

  16. Nichole August 14, 2013 at 8:36 pm #

    Thank you for writing this comprehensive and informative article on VBL’s. I am currently doing a bit of research on how to stay warm at night for an upcoming trip to Nepal and I have found your posting to be very helpful.

  17. Paul French October 26, 2013 at 10:57 am #

    Andrew,

    What a tremendous article . 10 Stars all around!
    Were the heck were you 40 years ago when I lived in Michigan, had no understanding of any of these concepts and absolutely no money to test things besides garbage bags and cheap plastic K-mart lose-weight work-out suits? So poor that cotton long underwear (Collon long underwear under a plastic suit was nearly an actual killer) and cotton insulated, used bedrolls or Military surplus was all I could afford.

    For 25 years I have lived in Texas but hope to do a Canadian week with only VERY moderate physical effort goals next year (in my 60′s). When you make you VB clothes such as the jacket do you make elastic “sealers” so to speak to prevent vapor loss at the waist, neck and wrists or what?

    Thanks very much again.
    Paul

  18. shane October 31, 2013 at 7:35 am #

    Great article Andrew,

    After the success of a VBL in my sleeping bag last year, and plastic bags on my feet I’m taking the RBH VBL jacket and socks out to play this winter :). My only concern is damp feet 24 hrs a day for the longer legs (1-3 weeks).

    Time will tell :)

    • Andrew Skurka October 31, 2013 at 8:45 am #

      So long as you are not a prolific sweater, and so long as you take steps to avoid excessive perspiration, you should be fine, especially if you take every opportunity to dry out your next-to-skin layers, like when you build a fire, when you get an abnormally sunny and warm day, or find a shelter to get inside out of the cold.

    • Duncan Coolidge November 20, 2013 at 12:51 pm #

      For the damp feet issue try using an actual paste antiperspirant for several days prior to your outing. You can do the same for your hands. As for your torso and legs meticulous exertion control and venting are necessary. One benefit of the vapor barrier is early detection of overheating for the level of exertion and insulating layers being worn. Fortunately that moisture never reaches your insulating layers.

      Best regards,

      Duncan

  19. Andrew October 31, 2013 at 1:44 pm #

    Great article and very informative!

    I will be climbing Elbert or Massive in January/February and anticipate lows around zero degrees F or possibly below. I have a 5 degree 800 fill down Marmot bag that I have taken down to the 5 degree rating wearing only midweight synthetic long underwear and was quite comfortable. Based on your article it appears that a VBL could be applicable to my trip as the temps will be cold with very low humidty and dew point. Would/could a VBL help close the small gap in temperature?

    Would the VBL in the link below work? I live in Texas and I don’t go on many winter trips so spending $100 on something I might use once every few years seems like a waste.

    http://www.campmor.com/vapor-barrier-liner-long.shtml

    Thanks for your help,

    Andrew

    • Andrew Skurka October 31, 2013 at 2:06 pm #

      For how many nights will you be out there? If just one or two, I would not bother with VBL clothing or a sleeping bag liner, as the moisture accumulation will be minimal over that time period. Plus, if you are in a big group shelter it may be warm enough in there to dry out your stuff.

      I would still consider VBL mitts — sweat-soaked mitts get really cold by the end of the day.

      • Andrew October 31, 2013 at 2:30 pm #

        We will be out there for 2 nights, 3 at the most but I will be in a 2 man mountaineering tent. On my last winter climbing trip I noticed that ice had formed inside my sleeping bag and was freezing even though the outside temp was only 10 degrees and I was in a zero degree bag. I ended up taking that sleeping bag back to REI but now I’m curious if this was my sweat freezing in the bag? I guess this is my main thought behind going with a VBL as that was a truly miserable night. Also, I will definitely check out the VBL mitt.

  20. AlexeyD November 18, 2013 at 11:30 pm #

    Hi Andrew,

    Thank you for this article. I did want to point out one issue with your discussion of dew point and condensation. Dew point is a function of two variables: the actual temperature, and the relative humidity. Unless RH is 100%, the dew point will always be LOWER than the actual temperature. Because the temperature across your sleeping system is not constant, but rather a gradient, the dew point will likewise be a gradient, and whether or not condensation will take place inside your bag will depend both on that gradient and on the amount of moisture entering the system (i.e. how much you are perspiring), as well as the porosity of the outer sleeping bag fabric.

    Just as VB requires careful thermal management, it’s also quite possible to manage the amount of moisture buildup in a non-VB sleeping system by avoiding overheating. In that regard, your point about wearing extra insulation layers under your sleeping bag is well taken: that extra layer creates an additional temperature gradient between you and the insulation in the bag, making condensation inside the bag (or even in your layers) more likely. I’ve found that, for the most part, trusting the bag to keep you warm down to its “comfort rating” with minimal or no layers, as daunting as it may seem when you first get into a frigid tent, pays off in the end, and will usually result in a comfortable night’s sleep without having to deal with a damp VB liner, and with little or no condensation inside the bag.

    Our bodies are designed to shed a certain amount of moisture, even when sleeping and not overheating. Thus, in my opinion, the optimal sleeping system is one that allows for such “routine” moisture loss without compromising its insulating properties.

    I have us

  21. Tim November 19, 2013 at 9:13 pm #

    Could a very thin (0.5mm) neoprene wet suit like NRS Hydroskin be used as a VBL?

  22. Kyle November 28, 2013 at 3:41 pm #

    I know this article is old but the information is timeless – hoping you may still reply…

    In the article you said you prefer a polyester-based base layer because it absorbs less moisture. In some of your replies to comments, it seemed like you had an argument for wool because it’s anti-microbial. Can you help clarify? Are there different situations / conditions where one is preferred over the other?

    Also, reading between the lines it seems that on a multi-day cold-weather excursion, you may never take the VBL off? Is that correct? Do you ever air out your base layer? How long can you go without getting trench foot?

    • Andrew Skurka November 29, 2013 at 9:27 am #

      Re wool versus synthetic. A synthetic base layer will dry faster; a merino layer will smell less. They’ll both work underneath VBL’s. Personally, I use wool, and I’ve used up to 195 g/m2 weight with satisfactory performance.

      Re multi-day use. Your VBL top and bottom should have vents (e.g. front zip, forearm zip, side hem zip) so that you can air out easily and quickly; VBL’s without such vents are a disaster waiting to happen. Also, much of the moisture accumulates on the inside layer of the VBL, so when it’s cold enough you can quickly take off the VBL, let the moisture freeze, and then shake off the frozen moisture.

      Socks are harder since they can’t have vents and since you can’t take them on and off easily. For me at least, it worked fine to remove them at the end of the day when I arrived at camp. My liner sock usually would be damp, but it would dry out overnight. Yes, I’m aware that moisture probably ended up in my sleeping bag, but overall it was a minuscule amount, especially since I could usually dry them out some before going to bed.

      • Kyle November 29, 2013 at 6:51 pm #

        Thanks for the quick reply. Regarding the sock liners – I guess they’ll dry pretty quickly if you can build a fire. Otherwise – worst case – I suppose changing out and carrying a few pairs of frozen liners is better than having wet feet for multiple days and nights.

        Thanks again – very informative.

  23. Amelia January 20, 2014 at 6:10 pm #

    Hi Andrew,

    Thanks for all the great info. You’ve done a wonderful job at explaining something I, as a seasoned backpacker, just heard about for the first time in preparation for my first mountaineering trip.

    Like others, I too have winter camped and experienced dampness on my down sleeping bag and wondered why it was soaked in the morning.

    For my upcoming trip, I will be sleeping in a two person, 4 season tent (well ventilated, but heavy nonetheless). Previously when I winter camped with my -20 Mtn Hardwear down bag, the moisture accumulated on the outside of the bag, not the inside. Temperatures will likely be hovering around zero F, maybe lower. Humidity will be mild. Should I use TWO VBLs in my system or just one? I won’t be using a bivy in addition to the tent. If I just use one, should it be used inside or outside my down bag?

    Thanks for lending your helpful experience! :)

    • Andrew Skurka January 20, 2014 at 9:21 pm #

      Two VBL’s will not do anything more than one will.

      The VBL should be on the inside of your bag, so that insensible perspiration (aka sweat) cannot pass into your bag’s insulation. I recommend VBL clothing worn outside of your base layers but inside of everything else, so that you can wear all of your clothing to bed. If you use a VBL bag liner, however, you can only sleep in your base layers, and at best you can keep your clothing inside your bag but outside of the VBL.

  24. Greg January 27, 2014 at 2:09 am #

    Hi everyone,
    I have just come across this extremely interesting article and discussion … I am completely new to the concept of VBL and as such I would like to say thank you for this great article which has definitely helped me understand better the principles of VBL.
    However there are still a few things that confuse me, and I hope you won’t mind if I ask a couple of questions…
    So I get that the idea is to prevent any insulating layers of clothing (or sleeping bag) from absorbing the water which comes out of my skin, which is what will eventually compromise my gear’s ability to keep me warm. I also understand the need to manage the whole body temperature principle, and that one needs to learn to adapt and regulate the body temperature accordingly. But here’s my question: isn’t a layer of VBL against my skin going to make me sweat even more? Even if i make sure to remove layers so I don’t overheat, I have the feeling that the plastic layer would cause a lot of sweat to accumulate between my skin and the VBL itself, and then where does this water go? Sure it won’t penetrate my fleece or down jacket, but what happens to it then? I get that VBL is best suited for very cold environemnts and situation, but take the Ski example. This was very well described, I have experienced it all my life as a Skier, once the sun drops down behind the mountains, the temperatures fall dramatically, and you get really cold very quickly as your clothes are all wet from a day’s intensive skiing…. but if i had been wearing a VBL, while skiing, I’m pretty sure it would have caused me to sweat a lot too, if not more, then where would all this sweat go? Or is the idea that basically we assume that I would have removed enough of my gear during the day that I wouldn’t have sweated?
    This is all really fascinating though, I know that I will try and learn properly about VBL so I can put it to test as soon as possible….
    Thanks in advance for your help!

    • Andrew Skurka January 27, 2014 at 4:36 pm #

      Three things.

      1. The VBL will make you more sensitive to your perspiration, and you’ll adjust your layers to minimize it. If you have adjusted your layers are much as possible and you’re still sweating, then you’re probably wearing VBL’s when you should not be, i.e. it’s too hot for them. So so long as you manage them properly, you’ll sweat less, not more, with VBL’s.

      2. Even if you manage your perspiration closely, you will still sweat, and it will still collect inside the VBL’s. To avoid excessive collection, you need to air out your VBL’s occasionally. For instance, if I notice that my hands are overheating in my VBL gloves, I remove the gloves and clip them onto my shoulder strap, and ski instead with just my liner gloves, which will have collected a little bit of moisture. But within a few minutes, this moisture has evaporated and I can put my hands back into my gloves.

      3. Don’t wear VBL’s next to skin. Instead, wear a lightweight layer between your skin and the VBL. This will add comfort without reducing your ability to sense excessive buildup of perspiration.

      • Greg January 28, 2014 at 1:29 am #

        Great, I see what you mean, I’ll try and put that into practice.
        Thanks a lot for your reply, and thanks again for sharing your knowledge!

      • David Markun May 7, 2014 at 4:50 pm #

        Thank you for your writings on VBL. I think I first came across a basic statement of the concept in a magazine over 40 years ago. I am surprised that it has not yet become mainstream in the recreational equipment industry. Instead, all these decades later, you are a pioneer. Thank you for that.

        I am remembering, from what I read over 40 years ago, a claim that there is a bodily feedback mechanism that reduces perspiration output (even of insensible perspiration) when high humidity is sensed on the skin. That is in addition to the conscious adjustment of clothing and the regulation of effort which you describe as methods to control sweating. Such a bodily feedback mechanism seems plausible from an evolutionary perspective (no point sweating if it’s not going to cool you off). If such a mechanism exists, then VBL would conserve water and electrolytes, as well as body heat.

        Obviously from what you report, under heavy workload this putative feedback mechanism is not enough on its own to control sweating sufficiently. Perhaps, though, such a mechanism could make a significant difference during low effort times such as sleeping.

        Best regards,
        David, who has not experimented with body-wide VBL but likes neoprene socks

  25. Gerald Dugan February 1, 2014 at 10:37 am #

    Andrew,

    I am looking at materials to make a hybrid sleeping bag/quilt.

    The bottom of the bag will be unlined. I am looking at a 30D silnylon material due to its waterproof nature. An air or foam half mattress will provide for insolation for the torso.

    For the top:

    Insulating material will be 990 fill down.
    I was thinking about using eVent or HyVent material on both sides. This should prevent moisture from passing thru the material into the down. It in theory would also allow for any moisture that did reach the down to pass thru the material when I hung it up to air and dry out. Both are three layer materials which make them slightly heavier (1-2 oz per square yard). Weight is not the primary concern.

    In an emergency this setup could be used alone as a bivy or an injured person could be put in the bag and onto a sled for evacuation.

    I enjoy and do a lot of cold weather solo (not many people want to have this much fun) hiking.

    One concern is this may lock in too much vapor. I normally sleep in just a base layer and vent the bag when I get warm. Clothes, and water bottles are kept in the bag to prevent freezing at night. Leaking water bottle a potential but so far has not occurred.

    I need to add vapor barrier socks between liner and insolation layers.

    Please any advice/thoughts are greatly appreciated.

    Very respectfully

    • Andrew Skurka February 4, 2014 at 9:08 am #

      “I was thinking about using eVent or HyVent material on both sides. This should prevent moisture from passing thru the material into the down. It in theory would also allow for any moisture that did reach the down to pass thru the material when I hung it up to air and dry out.”

      Your understanding of these fabrics is inaccurate. Both are classified as “waterproof-breathable,” which is a smoke-and-mirrors term for a fabric that supposedly prevents moisture from passing through it while also allowing moisture to pass through it. Huh, what? That’s called marketing.

      In reality, these fabrics do breathe, albeit not nearly as well as, say, a base layer shirt or the lightweight shell fabrics you see on most sleeping bags today. So when you perspire at night, this perspiration will pass through the inner fabric, into and hopefully through the insulation, and through the outer fabric, where it will evaporate. This assumes that your perspiration doesn’t hit the dew point as it is passing through the bag, in which case it will condense onto the insulation or the shell fabric.

      Fabrics that breathe as such, even at a restricted rate, do NOT function as vapor barrier liners. A VBL fabric performs more like the 30D silnylon you are planning to use for a floor — it is waterproof but not breathable.

      Personally, I prefer bags that use highly breathable nylon or polyester shell fabrics. They are lighter and less expensive than WP/B fabrics, and MUCH more breathable. I’m not concerned about the lack of “waterproofness” — my shelter serves this function extremely well, and WP/B fabrics aren’t that waterproof anyway.

  26. Bill Fay February 9, 2014 at 12:59 pm #

    Andrew,

    thanks so much for this really detailed and informative article. I’m heading to Lapland then Svalbard in 10 days, and trying to prepare for the conditions.

  27. Zbynek March 1, 2014 at 4:58 pm #

    Hi

    How about using a space blanket as a liner for sleeping bag? There is possible to buy it as a sack. It is very light. If needed, using lightweight pack tape, you can built in some cord for tightening around a neck.
    We can also make a suit from the space blanket. Just using pack tape. And some bungee for tightening around waist, for pants and/or shirt.
    Everything will be light, and cheap. It looks like it will not last for a long time, but maybe enough long.

    • Andrew Skurka March 3, 2014 at 7:43 am #

      Mylar, the material from which “space blankets” are made, is non-breathable and will therefore is suitable for use as a VBL. However, as you pointed out, it’s not very durable and will not last as long as, say, polyurethane-coated nylon.

  28. MB1 March 21, 2014 at 6:25 pm #

    So why not a down sleeping bag where the down is enclosed in a non-breathable waterproof shell?

    In such a case, moisture produced by the body would not enter the insulation (in the morning, the accumulated inner moisture could be wiped dry by a lightweight towel to then be frozen followed by a defrosting-by-shaking). Moisture from any source outside of the bag’s external shell could not enter insulation.

    …just speculatin’.

    • Andrew Skurka March 21, 2014 at 10:07 pm #

      At least one side of the bag would need to be breathable, or else the bag would resist lofting after being compressed, or compressing after being lofted (because a non-breathable fabric does not allow air to pass through it, so basically air flow would be limited to the seams).

      This breathable side could not be on the inside, adjacent to the sleeper, since moisture would accumulate inside the bag against the non-breathable layer.

      The breathable layer could go on the outside, and the non-breathable layer adjacent to the sleeper, but the problem here is that the sleeper would not be able to wear any clothing to bed besides a base layer. Otherwise, perspiration would collect inside their clothing system, e.g. puffy jacket.

  29. MB1 March 22, 2014 at 6:58 pm #

    Thank you for your erudite and concise feedback – nice!

    Your input, combined with my initial – and trés naive – speculative suggestion, I’m going to employ a sleeping bag manufacturer who can customize a bag to incl. some of the following design and material specifications (barring further developmental suggestions, admonitions, tweaks and mods)

    -Mummy bag w/ allowance for extra clothing layers that include a base layer, a VBL suit, and a top ‘n bottom ‘puffy’. (Per VBL cothing: a ‘stretchy’, durable, lightweight, and waterproof material just has to be out there in this Age of Obama.)

    -Non-breathable and waterproof inner & outer shell fabric. Light weight and reasonably durable à la a Pertex Quantum et al.

    -Vent panels (for the purpose of compression & lofting) comprised of an eVent-type material, mapped perhaps to be integrated with the outer shell on each side of each baffle. Given, these side ‘apertures’ will impinge on the absolute protection of the insulation from water but it should reasonably reduce the volume of water that the insulation is exposed to such as is seen in a ‘breathable’ bag. (Sea To Summit employ a variant of this construction in their eVent Compression Dry Sack).

    -Order a tailored VBL suit that doubles as both a daily wearable and a sleeping garment when extra clothing is to be worn in the sleeping bag.

    I believe I’ve found a European-based cottage industry manufacturer of sleeping bags to construct the bag once I’ve chosen materials and settled on a rough design. Given, Im still in round Naive.0 of my open sourced conceptualizing but I can’t shake the urge to both theoretically and practically tinker about with the vision of VBL and non-degradable sleeping systems in the context of extended forays in to the freezing wild.

    But sure – nano-technology will probably come along and make the above line of reasoning a completely irrelevant approach before I come anywhere near achieving an ultralow-degrable cold weather sleeping solution. At least the down i invest in this little project can always be recycled into something actually useable.

  30. MB1 March 22, 2014 at 7:54 pm #

    Just one more question apropos your, “Otherwise, perspiration would collect inside their clothing system, e.g. puffy jacket.”

    Would it really, considering that the dew point would be somewhere within the sleeping bag’s insulation? I would surmise that the vapor would ‘want’ to travel right through the clothing system and outward along the temperature and humidity gradients to some (dew)point found deep within the sleeping bag.

    Unfortunately for Mr. Vapor however, the outward bound water vapor would speed right in to a proverbial brick wall when it reached the sleeping bag’s waterproof inner shell. Perhaps then a VBL-suit would not be needed at all–just an outer shell on the puffy that was breathable yet markedly ‘waterproof’, e.g. Pertex Shield+, a Gore-Tex, et al. This then to prevent back-travel/absorption of the accumulated liquid at the bag’s inner face back into the clothing’s insulation from whence it first came. Certainly the humidity in the milieu between the puffy’s breathable yet ‘waterproof’ shell and the truly waterproof inner shell of the sleeping bag would not become so great during a night’s sleep that the body’s outward bound perspiration would be stopped from penetrating outwards through the puffy’s shell, i.e. the puffy’s shell stops breathing…or?

    It’s perhaps getting rather esoteric here but I’m game to be corrected and educated if you can spare your time and wisdom to shape my understanding of these mysteries.

    • Jeffrey Cooper March 29, 2014 at 6:47 am #

      Here is my problem. My feet are always cold when I ski. I have had three ski boots and at the end of the day my feet are wet or dam. I presume its due to sweat which makes my feet cold. Which is a better solution to warm my feet.
      Vapor barrier linings or hotronics foot heaters?
      How will vapor barrier liners work in a ski boot which is totally enclosed?
      Thanks for your help

      • MB1 April 1, 2014 at 8:14 pm #

        Hi Jeffrey.

        Why not try out both your suggested solutions (VBL and Hotronics) and see what works best, if at all, for your feet? Nothing like field tests to move beyond metaphysical deduction.

  31. MB1 May 22, 2014 at 7:43 pm #

    First version of VBL-bag built (though it has yet to be placed in true harm’s way); silnylon inner and Pertex Endurance outer. Lofts well enough and weighed the same in the morning after I spent the night camped out on one of my balconies as it did when I hit the sack 8 hours earlier. I tried it out on a night I had a flash fever from some flu-ish bug.

    I chomped down some paracatamol an hour after hitting the sack and sweated off the fever in the bag. The night temp was approx. -7C and the bag was filled w/ ca. 450 grams of CUIN 850 (Eur) down, with 65% distributed in the upper baffles per design specs. Sleeping on a Neoair Xtherm, I knew being warm wouldn’t be a challenge given the parameters of the test which included donning a lightweight merino wool base layer (top ‘n bottom).

    Yes, I was damp come morning – but comfy so. Far from proof of concept to be sure, but not too discouraging either.A week in Svalbard next!

  32. Tim May 29, 2014 at 2:05 am #

    Hi Andrew,

    Thanks for sharing your knowledge with those of us who are less experienced. I am currently in the planning process of making my own vapour barrier clothing. How do you close off your vapour barrier system so that the humidity doesn’t escape into your insulation layers? Are elastic hems sufficient? Or should I be using a slip lock buckle to obtain a tighter fit? I thought a slip lock buckle or piece of cord might be a good way to go, however, I was concerned that I might reduce my circulation in obtaining and adequate seal. How essential is this seal? Also, have you made yours so that your pants and top can zip together? Or is this somewhat unnecessary?

    Thanks in advance,

    Tim.

  33. Jonathan September 9, 2014 at 8:07 am #

    Hi Andrew,

    After reading your article and doing some research of my own, I discovered that it’s possible to purchase chemical protection coveralls that are impermeable to water vapor as well as other gases. The suits are made out of a material called Tychem, which is Tyvek treated with some sort of gas-proof coating. I have a hunch that these suits would work pretty well as VBLs, but since they’re intended to be worn over clothing they’re very baggy. Do you think that would create any problems?

    Thanks!

    • Kevin Sweere November 20, 2014 at 8:09 pm #

      Wrt Tychem suits as VBLs, they’re certainly cheaper than most VBLs ($16 vs $40) and more roomy than a mummy. They take a bit more time to put on than if you were to just slide into a mummy. During the day, don’t forget to turn them inside out and dry them out.

  34. Kevin Sweere November 20, 2014 at 8:14 pm #

    For a cheaper, silnylon DIY mummy liner buy a silnylon tarp (e.g. http://www.aliexpress.com/snapshot/6361462776.html ) for $10 then sew it up into a bag. (Pretty simple.) Weighs about 150 grams.

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  5. anyone use the Vapor barrier method for cold feet? - Page 2 - December 12, 2013

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