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When camping in rainy/high humidity weather (without direct sunlight) should you still air your down sleeping bag in the morning or stuff it directly? Obviously not in direct rain, but what about under a roof when humidity is above, let's say, 90%?

My guess is stuffing directly is better as your body heat helpt evaporate some water, by letting it cool and "dry" it will attract condensation again and end up wetter, but so far don't have numbers to support this.

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    Remember that airing isn't only about moisture, but also about freshening out body odours. If you are going to stuff it immediately at least manipulate it a bit (squash out the air by rolling a couple of times) to exchange the stale air in it.
    – Weather Vane
    Commented Jul 23, 2023 at 9:48
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    You body is quite a source of moisture, don't forget. A warm person in a sleeping bag in cooler air will make it slightly damp, especially as the night time humidity will also be high
    – Chris H
    Commented Jul 24, 2023 at 11:59
  • Wind helps a lot. But usually turning the sleeping bag inside out and hanging it in non-rain gets rid of moisture and somewhat body odors.
    – Vorac
    Commented Aug 9, 2023 at 15:31

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You should still air it. Your body heat will, indeed, help evaporate some moisture but will generate more over the night.

A human body generates the same heat as a 100-watt light bulb but it's also creating humidity. It's so bad that during WWII when the Germans created massive shelters for thousands of people, the humidity generated by the bodies was so bad that it could rain inside and they had to improve the ventilation system by a lot.

Studies from the Canadian Military showed that the weight of a sleeping bag can increase by 30% because of human moisture, and this....in the Arctic! Also, if you stuff it immediately, you'll stuff it with moisture. That's bad! So always air dry your sleeping bag as much as possible.

Also, always use a liner to prevent your sleeping bag from becoming dirty inside. If it does, it'll clog it and there'll be more moisture inside. In winter, you can even use a moisture barrier. Oh joy of the down sleeping bags! :)

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  • This mostly seems to address the general importance of air drying a sleeping bag which is clear, but does not address the particular case of a warmer sleeping bag being able to dry in high humidity (whilst cooling down, potentially causing condensation). Maybe the question is more suited for a physics oriented exchange since it's more about the interaction of the sleeping bag cooling down and relative humidity of the surrounding air.
    – bobcatfry
    Commented Aug 29, 2023 at 15:06
  • You seem surprised that the bag collects a lot of moisture in cold conditions. It will collect more there than somewhere warmer, because the inside air is close to body temperature and moist, while the outside air is much cooler. So when the inside air reaches the outer shell of the bag, it will be cooled and the moisture will condense. If this wicks through the outer layer, it will evaporate slowly in cold conditions (especially in still air, and in the cold you really want to get out of the wind)
    – Chris H
    Commented Aug 30, 2023 at 7:57

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