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-mil 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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Posted in , , , on November 7, 2017


  1. JD Dallager on 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 on 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 on 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 on 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 on 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 on November 7, 2017 at 9:40 pm

    What type of rain poncho is that blue one?

    • Andrew Skurka on 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 on 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 on 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 on 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 on 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 on 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 on November 21, 2017 at 12:04 pm

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

  4. John Joyce on 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 on 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 on 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 on 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.

  8. Kajungizmo on January 5, 2019 at 10:13 am

    Great video as always! One minor technical critique – trash compactor bags (or any other plastic sheeting material) is not measured in mm (millimeters) of thickness. They are measured in Mils, which represent thousandths of an inch. 2 Mils is 0.002″, not 2 mm.
    Thanks for all your useful tips and insight!

    • Andrew Skurka on January 5, 2019 at 2:26 pm

      Ah, that makes total sense. Thank you very much.

  9. Mark A on January 22, 2019 at 9:02 pm

    Hey there Andrew,
    I know I’m coming late to the party, after only finding your site about a year ago, but at least I’m here now!
    As a Brit expat living in Queensland, I’m hoping for your thoughts on the old Down v Synthetic sleeping bag. Summer trips can be nights of upper 20C with humidity from 60-90%, whilst shoulder seasons in the lower states can easily hit subzero temps. Added to this, trips planned for NZ spring and back up to Scotland for European summer.
    Budget is limited, I don’t really want to have multiple sleeping bags (although i use a liner or cowboy camp during the hottest nights in QLD), but I’m now a bit stuck, as just toooo many choices, options and considerations for the variable conditions?
    I’m in the process of renewing my whole kit, so my options are pretty much wide open.
    Any pointers would be great.
    Since finding your site, the info, guidance and knowledge you’re passing on to the rest of us is invaluable.

    • Andrew Skurka on January 26, 2019 at 5:25 pm

      I generally discourage purchasing one piece of gear that covers all of your wide-ranging needs. It ends up sucking at both. The exception is if you have a limited budget and/or you’ll never be more than a casual user.

      Sleeping bags are one place where I recommend spending some money. It’s like a good chef’s knife — cry once, buy once. The best place to be is just short of where prices dramatically increase for marginally better products. Western Mountaineering makes beautiful bags, for example, but they’re 2x as good as Sierra Designs bags.

  10. Eric B. on April 4, 2019 at 10:07 pm

    By testing loose down (from Ripstop By The Roll) treated with the same DWR that The North Face uses I found that a 3″ x 3″ “hunk” of down in a highball glass of water is amazingly water resistant.

    I put the down in the glass and filled the glass 1/2 full by SPRAYING the down with the kitchen faucet .
    The down stayed dry! And NO down went below the miniscus level of the water for 3 days! I’m just amazed.

    My LL Bean -20 F. goose down bag has “DownTec” DWR, my Bauer down vest and -40 F. PEAK XV expedition parka have “Dri Down”.
    My older Eddie Bauer light down jacket and Western Mountaineering overstuffed Megalite mummy bag have no DWR so I’m very careful with them, airing them when ever the weather permits.

    I dunno what the differences in the hydrophobic properties of various DWR brands are or their comparative longevity but I’m hoping repeated stuffings of the garments do not affect either.

    i do have older DuPont Thermolite Micro insulated jacket and pants from my days tree stand hunting in N.W. Pennsylvania so I cause them if necessary. They are quite warm under Gore-Tex parka and pants when using a medium weight polyester long johns base layer.

  11. Alex on April 26, 2019 at 6:21 am

    Hey, I was hoping someone could give me a few tips on getting a new sleeping bag. I’m going to go with down but I live in St. John’s, NL, and it’s a pretty humid environment with 80 + percent humidity mostly all the time. I was gonna go with a three season bag as I already have a relatively warm and light synthetic summer bag.

    I’ll be camping in temps close to 0 C or a bit below in the shoulder seasons. Basically my question is should I go with a bag rated for around -6 C to account for the humidity and loss of loft? And is it worth it to invest a little extra to get hydrophobic down? My sleeping bag won’t get soaked but it will probably get pretty damp based on the humidity and the proximity most campsites have to the ocean. I line my bag with a waterproof bag as outlined in the article but I’m wondering how much moisture the bag will take on at night in my tent, as I’m sleeping. I’ll also usually have a chance to dry it out in the morning and most trips won’t be more than 3 nights.


    • Andrew Skurka on April 26, 2019 at 8:37 am

      Even if humidity is 80 percent in the winter, there is still much net moisture in the air at 0 degrees C than at 30 degrees C. That’s why hands and lips tend to dry out in the winter — there’s less moisture in the air.

      In temps around 0 C with high *relative* humidity, you actually have two concerns. The first is ambient humidity; the second, insensible perspiration that may hit the dew point before it can move through your bag and evaporate into the air. This will essentially make your bag damp from the inside.

      To answer your question, yes, I think you should buy a bag that’s a little warmer than the lowest temperatures you normally expect to encounter, so you have some margin on the second and third nights when your down isn’t as lofty as it was in your dry and warm house. You can also use clothing to help you push below the normal comfort range.

  12. Terri on January 30, 2020 at 2:23 pm

    Hi Andrew!
    I am hiking the Northern AT/Benton Mackaye Loop in the Great Smoky Mountains National Park this September. In that environment/time of year, would you recommend a synthetic or down jacket? I (like you) always bring a light fleece and rain gear in addition to my hiking clothing. I am worried about the humid/wet conditions and am cold by nature. The down jacket would be an REI 850 fill Magma vs an Enlightened Equipment Torrid. FYI, I already own the Magma and wouldn’t be out any money.

    • Andrew Skurka on January 30, 2020 at 3:53 pm
      • Tre on January 30, 2020 at 4:20 pm

        Lows in the 40s, highs in the 70s. High humidity with average 8 days rain per month. The Magma does have treated down. The Torrid has Climashield Apex insulation.

        • Andrew Skurka on February 2, 2020 at 11:57 am

          I think you could probably go either way and be fine. I would probably make the choice based on (1) what I already owned and (2) what would serve me better overall for this and other trips. So, in your specific case, I’d stick with the Magma.

  13. Terri on February 2, 2020 at 11:54 am

    Andrew, did that give you enough detail for a recommendation?

  14. Terri on February 2, 2020 at 12:01 pm

    Thank you. This is a different environment for me so I was feeling uneasy.

  15. Tina on September 2, 2020 at 1:55 am

    Hi Andrew,
    thanks for your advice.
    I´d like to ask you for a recommendation: I live in Indonesia, where humidity ranges between 70%-90%. However, I often hike at high altitudes, where it can get really cold. That´s why I´m thinking about buying a down insulated sleeping bag rather than a synthetic one. I just wonder whether a down sleeping bag could be destroyed be being constantly exposed to such a high humidity. What do you think?
    Thank you.

  16. Eric B. on September 2, 2020 at 10:43 am

    Like the nearby Philippines where my wife is from and where I lived as a Peace Corps Volunteer the humidity requires a light synthetic fill bag or quilt. A quilt actually would be more comfortable IF you have a sheet type cover for your mattress. Sleeping on a bare mattress would be “sticky” in that humidity.

  17. Tina on September 2, 2020 at 11:14 am

    I hike a lot at altitude of 3000m above sea level, where it can get really cold, around 5 degrees Celsius. That´s why I consider buying a down sleeping bag.

  18. Eric B. on September 3, 2020 at 1:59 pm

    In that case I would go for a down bag, not a quilt. And that down should have a good DWR down treatment like Dri-Down or Down Tech.

    LL Bean has some excellent bags with DWR treatment. I have their -20 F. down bag and it is the best designed of the 3 other winter bags I have owned.

    I bought some DWR treated loose down for repair purposes and tested a highball glass sized amount in a glass. I ran water OVER it until the glass was 1/2 full. I let it set for about 4 days and the DWR down floated on top and never absorbed water, even the water I ran over it on the initial filling of the glass. Good enough for me. BTW, that DWR was the same type The North Face uses on their down products.

  19. Taylor on November 18, 2020 at 10:46 am

    Hey Andrew, those are great ideas. Wonder what you think of the idea of using a thin synthetic outer bag and a down inner bag? I tend to get a little cold towards morning in my down bag I think as hours of moisture build up and finally start collapsing the down a little and the temp drops to the lowest point. I’m thinking the synthetic out bag would keep the outer layers of the down warm and dry and the moisture could condense on the synthetic but it won’t collapse so it should theoretically stay warm right?

    • Andrew Skurka on November 19, 2020 at 6:56 am

      This two layer system would be better than just one down layer, but don’t be too optimistic: a synthetic layer that has moisture in it will not be as warm as a dry synthetic layer.

  20. Eric B. on November 18, 2020 at 11:50 am

    Taylor, your idea of a synthetic outer bag is one that has been used before and it usually works as the body vapor condenses in the colder outer layers.

    If you don’t want to use a VBL bag or VBL garments then this would be the next best approach.

    The main reason the Scott Antarctic expedition failed is that their down “sleeping robes” became increasingly laden with frozen body vapor and useless. The other reason was lack of food supplies.
    There were many reasons why the Norwegians easily made it to the South Pole and back to their base and the Brits did not.

    • Taylor Anderson on November 18, 2020 at 12:50 pm

      Interesting, think maybe I will try pairing two Mountain Hardwear 30 degree bags this way and give it a go…I carry a vapor barrier but only for emergencies, never actually tried it maybe I should.

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