Stay warm when it’s wet: How to protect down insulation from moisture

When shopping for a sleeping bag, insulated jacket, or insulated pants, you will have a choice of insulations:

  • Down, which is a commodity product measured by fill power, e.g. 800-fill; or,
  • Synthetic, which is normally made of interwoven plastic fibers and which may be marketed as Primaloft, Climashield, or a proprietary version like TNF Thermoball.

Given current technologies, I believe that down is still the superior choice for performance. It’s warmer for its weight and more compressible, and has a much longer lifespan, making it a better long-term investment. Premium sleeping bags, in particular, can nearly be family heirlooms.

Synthetic insulations have one decided advantage: they are less expensive. They also retain more warmth when wet, on a relative basis. However, when the thermal superiority of down insulation is accounted for, synthetic’s wet weather advantage may be a wash — a damp down sleeping bag can be just as warm as a perfectly dry synthetic bag of the same weight, because it’s original warmth was so much better.

While synthetic insulations are frequently marketed as being “warm when wet,” this claim defies the laws of physics. If your synthetic sleeping bag or puffy layers are wet, the thermal mass of that wetness will steal your body heat. Period.

Down insulation can get wet from both precipitation and ambient humidity. Here are four techniques to mitigate these factors:

1. Water-resistant down

Down can be treated to be made more water-resistant. The process adds little cost to the down, and actually improves loft. Water-resistant down — which may be branded as DriDown, DownTek, or others — will not be warm when wet, but I find that it holds up better in humid conditions and that it dries faster than traditional down.

2. Pack liner

I protect my sleeping bag and puffy layers using a Brute Super Tuff 20-gallon Trash Compactor Bag made of 2-mm plastic. Scented bags can be aired out, if it bothers or concerns you.

In very wet environments, I may use two bags: one to protect everything that I will not need until camp (e.g. sleeping bag, sleeping clothes, pad, stove, food for the rest of the trip) and a second bag for things I may need throughout the day (e.g. today’s food, puffy jacket, rain gear). If my shelter is wet, I keep it inside the backpack but outside the pack liner.

To waterproof my gear, I line my pack with a 20-gallon trash compactor bag. A wet shelter or raingear can be stored outside the pack liner but still inside the main compartment.

3. Mid-layers and sleeping clothes

On rainy trips, I will bring a mid-layer fleece like the REI Quarter-zip Fleece Pullover plus low-performance sleeping clothes made of polyester, wool, or fleece.

The mid-layer is worn between my hiking shirt and rain shell in cool-and-wet or cold-and-wet conditions, which preserves my down jacket for rest stops and camp. The fleece dries quickly and buffers moisture more effectively than a down- or synthetic-insulated garment.

The sleeping clothes guarantee me nighttime comfort, and prevent me from having to sleeping in my wet hiking clothes, which would then wet my sleeping bag.

Flyin’ Brian Robinson atop Yosemite’s Mt Whorl (12,033 ft) in late-September, wearing a 100-weight Patagonia R1 fleece top

4. The reset dry

This technique is my favorite and the most effective. If I get whacked with wet weather and become either uncomfortable or near the safety limits of my systems, I will take the first opportunity I have to dry out. Depending on the location and time of year, the time necessary for a reset dry will vary. On a sunny, warm, and arid late-morning in the Mountain West, it can be done very quickly. If you’re hiking the Appalachian Trail in February, you may need a motel room.

The reset dry is easy: expose ALL of your stuff to the sun, breeze, and dry air. Hang it in the trees, lay it on the grass, drape it over a boulder, pitch it haphazardly, etc. When things look and feel dry, pack it all up and keep moving.

A “reset dry” in the Alaska Range

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17 Responses to Stay warm when it’s wet: How to protect down insulation from moisture

  1. JD Dallager November 7, 2017 at 6:28 pm #

    Andrew: As always, your thoughts and shared experience/wisdom are insightful, pragmatic, money-saving…..and potentially lifesaving. Thank you!

    I especially appreciated your comment “While synthetic insulations are frequently marketed as being “warm when wet,” this claim defies the laws of physics.”

    It bothers me that the manufacturers get away with that kind of “false marketing”.

    That said, your four ways to protect down (and synthetic?) insulation from moisture are spot-on and most helpful.

    Many thanks again and keep on truckin’!

  2. Justin Baker November 7, 2017 at 8:45 pm #

    I think the best option if you are expecting wet conditions is to bring an extra warm sleeping bag. For example a (reliably) 15 degree bag in for 30 degree night time lows. This helps compensate for the inevitable loss of loft. If you are super toasty and comfy in your sleeping bag, then the sleeping bag will dry out from body heat very easily. In a super toasty, warmer than necessary sleeping bag you can dry out wet clothing without serious consequences.

    If I am camping in unexposed forests, I like to use a flat tarp. With a flat tarp, I can shelter myself from rain while still receiving heat from a fire. It’s easy to dry out a sleeping bag by building a big fire and sitting next to the fire with the sleeping bag wrapped around you like a blanket (body heat + fire heat).

    • Andrew Skurka November 8, 2017 at 8:35 am #

      Excellent suggestions. I have used the first one as well, surprised I didn’t think about adding that one.

      My personal experience with drying things by the fire is good, because I pay attention and I know how to build a fire that doesn’t product a lot of sparks. But I’ve seen a lot of other people burn up their gear doing this, so do it with care!

      • Mike November 8, 2017 at 1:51 pm #

        How do you build a fire that minimizes sparks? I’ve never heard of this before.

        • Andrew Skurka November 8, 2017 at 1:59 pm #

          Build the fire up and get a hot bed of coals, so that you’re not having to put wood on it all the time.

  3. Tage November 7, 2017 at 9:40 pm #

    What type of rain poncho is that blue one?

    • Andrew Skurka November 8, 2017 at 8:32 am #

      That’s the new Cagoule,

      Inexpensive, completely waterproof, lots of coverage. I wore the prototype but only got stuck in a single storm, and without properly sealed seams my experience was pretty awful. (Production shouldn’t have that problem.)

      • Peter H November 20, 2017 at 8:25 am #

        I have used the production version and been out for 2 hours in a light but constant drizzle and spent 30 minutes just standing in a downpour (yay hunting!). I stayed dry in both instances and didn’t get that all too familiar clammy feeling. Very happy with the value it provides.

        • Andrew Skurka November 20, 2017 at 8:27 am #

          Glad to hear.

          It’s a great piece for hunting. You can sit there in super crappy weather and have the precip roll off you, with no fear of membrane failure and without having to deal with separate jacket & pants.

      • Gement November 21, 2017 at 10:00 am #

        I know you are not SD Customer Service (I am already in dialogue with them) but what kind of fabrics/treatments do you expect when you describe something as fully waterproof? What conditions do you expect it to survive without getting you wet?

        My Storm Poncho that I just got from them, which I got it because I was going with the strategy of actually waterproof, structurally breathable, got my shoulders noticeably wet (well past clammy) after its first hour in drenching but not pounding rain. The customer service response was that it overwhelmed the DWR and that’s expected… which doesn’t sound “waterproof” to me.

        I would accept it as just the limitations of all fabrics and the hazards of living in the PNW, but what the two of you are describing sounds like it is better than that.

        • Andrew Skurka November 21, 2017 at 10:37 am #

          The SD Storm Poncho is made of waterproof/non-breathable material. When new, I would expect it to protect me from external precip. But I would also expect internal perspiration build-up in areas that get inadequate airflow, especially in humid conditions when the air has limited ability to absorb more moisture.

          How confident are you that the wetness you experienced inside the Storm Poncho was from external precip? I’ve never worn this product and I have not inspected it closely, but it wouldn’t necessarily surprise me. It’s a $50 item with a single-side coating of PU, probably 68d polyester, which is the most commonly used fabric in low-cost shelters. The hydrostatic head on the fabric should meet the minimum for being described as “rain proof” (I think it’s 800 mm), but that pressure may be exceeded by, say, shoulder straps and a heavy backpack.

          • Gement November 21, 2017 at 12:03 pm #

            Huh. Okay, good to have that confirmed. I am pretty confident it was external. I was walking hard enough for lower back sweat, but not a lot of pit sweat, and the side ventilation seemed like it was doing its job. I was not wearing a pack and would never trap a parka under a pack in any case.

            There were water droplets all across the inside of the shoulders when I flipped it inside out to see if the rapidly cooling wetness across my shoulders was a trick of the temperature change (when I walked into a restaurant and took off the parka).

            It sounds like you’re saying that’s not right, so this really might have been an individual failure.

          • Gement November 21, 2017 at 12:04 pm #

            Blah, poncho, not parka. But you knew that.

  4. John Joyce November 8, 2017 at 5:46 am #

    Love your videos! I’ve been watching a lot of your rain advice for my upcoming trip to Shenandoah!

  5. John Cl November 8, 2017 at 12:30 pm #

    Hi Andrew,
    Your comment on the SD Cagoule reminded me of a similar piece of equipment I obtained for the El Camino trail in Spain from which I just returned two weeks ago. It is called the Altus poncho from the high end Spanish company Altus which sells all sorts of outdoor gear in Europe. It is similar to a poncho except with a full front zip, arm sleeves, chest vents, hood, and an adjustable compartment in the back to fit over a pack. It is completely waterproof and not breathable. The construction quality is excellent.To my knowledge it is not sold in the U.S. but available in Spanish outdoor gear stores and also from Amazon U.K. from which I obtained mine. The price is reasonable and much lower than a full Marmot Precip jacket and pants set for example. Unfortunately I did not get a chance to use it on the El Camino due to the unusually warm and dry hiking conditions in Spain this year, but I did use it this spring in Northern California 3-4 times on day hikes during which it performed well with just slight but manageable condensation in the shoulder area.

  6. stephane November 24, 2017 at 7:09 am #

    For me, keeping my sleeping bag dry with a pack liner is the easy part. Where it gets tricky is keeping my bag dry when inside the shelter. Not from rain but from condensation and sweat that just can’t escape due to high relative humidity. I use a 15 degree bag and I have been in situation where the down collected so much humidity in a single night that I would have flirted with hypothermia the following night if I couldn’t dry my bag during the day. So campsite selection and shelter choice are just as important in my point of view as pack liner. Lately, I wondered how much influence on the loft sleeping in a vbl bag would have in these conditions. I live in eastern Canada and sometimes, it would be suicidal not packing my synthetic bag.

  7. Ewa Siwon June 27, 2018 at 11:35 pm #

    Hi, and what would you recommend for fastpacking in Lofoten (Norway). I’m going there in less than 2 weeks for one week and the forecasts are for a constant rain and low temperature 🙂 I’m going to sleep in a small SMD tent at camping sites but during the day I’ll be on my feet from the very morning until evening.

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