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Is it Warmer to Sleep Naked in a Sleeping Bag?

Sleeping Naked in a Sleeping Bag
Sleeping Naked in a Sleeping Bag

No. It’s a myth that sleeping naked in a sleeping bag is warmer than wearing in long underwear. I’m not sure how this Internet meme started but it’s dead wrong.

How Sleeping Bags Work

Sleeping bags are designed to trap the heat your body produces and prevent it from escaping. When you wear long underwear in a sleeping bag, you increase the amount of insulation between your skin and the cold air outside. This will make you warmer than if you sleep naked.

If that doesn’t make sense consider the following analogy:

A sleeping bag is like a house. A sleeping bag has insulation like a house that prevents heat from escaping in cold weather. Like your house, a sleeping bag has a furnace inside it that heats it up. In this case, its your metabolism which produces body heat. If you wear long underwear inside your house in winter, you will feel warmer than if you walk around the house naked. That is why wearing long underwear in a sleeping bag will keep you warmer than sleeping naked. It’s another layer of insulation that traps hot air and keeps it close to your body.

Exceptions to the Rule

There are times when wearing clothing in your sleeping bag will not keep you warmer. These are extreme exceptions, but I will list them here for completeness.

  • You wear so much extra clothing or fill your sleeping bag with so much extra stuff that you compress the insulation in the sleeping bag’s baffles and reduce the amount of warm air it can trap.
  • You wear such tight-fitting long underwear or socks that it reduces the blood circulation to your extremities and makes them feel colder.
  • You wear wet clothing which compromises the insulation in your sleeping bag as the heat of your body dries it. The moisture in your clothes doesn’t just disappear: it gets trapped by the sleeping bag’s insulation which degrades its effectiveness.
  • You wear too many clothes in your sleeping bag and sweat. As your sweat dries it degrades the insulation in your sleeping bag, just like wearing wet clothing. You’d have to sweat a lot for this to happen, so just de-layer or unzip your sleeping bag if you feel a sweat coming on.

Best Practice

The best practice is to wear a dry base layer (top, bottom, socks, and hat) in your sleeping bag at night to keep it clean and to keep you warmer in cooler weather. These should be loose-fitting to prevent your hands or feet from getting cold due to loss of circulation and to help trap warmer air near the surface of your skin.

While you can augment the insulation in your sleeping bag with an insulated coat or pants, you want to make sure that you can still move inside your bag and that the shell of the sleeping bag isn’t pushing hot air out of its own baffles. If your base layer is wet or damp, it’s best to dry it out before you get into your sleeping bag.

If you start to sweat at night, unzip your sleeping bag to cool off and re-zip it when you start to get cold. The amount of heat your body produces during the night changes, to a large extent based on how recently you ate food. So if you wake up cold at night, eat something sweet and fatty like a candy bar (without caffeine) or some nuts.

You have to understand that sleeping warm at night isn’t something that just happens. Your experience is very much influenced by the steps you take to sleep comfortably like wearing loose dry clothes to sleep, venting your bag when you’re too warm, or revving up your metabolism by eating something when you get chilled. Sleeping warm is a skill.

See Also:

REI: How to Choose a Sleeping Bag

The Art of Sleeping Warm at Night

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6 comments

  1. I think it depends whether you have a down or synthetic sleeping bag.

    With down sleeping bags, in my experience, the less you wear the warmer you will be. This is because down feathers need to be primed with your body heat in order to fully expand and reach optimum insulating efficiency.
    Wearing clothes inside a down bag prevents your body heat from activating the down feathers.

    This principle doesn’t apply to synthetic sleeping bags.

    • What? This is NOT correct. Heat does not ACTIVATE down feathers. Down and synthetic sleeping bags insulate you by trapping heat produced by our body in the air spaces between feathers or fibers. They work exactly the same way.

  2. I know when I started backpacking more than 30 years ago, there were no wicking baselayers. You had cotton or wool. Cotton gets damp and cold. Naked is better. Old scratch cotton made you uncomfortable, itchy and sweaty. Sweaty equals cold. Not so much a myth, more outdated.

  3. Well, i was obviously here because i was wondering about this topic. Like many people I heard that sleeping naked in a down sleeping bag was warmer, but i always had my doubts. One reason is that simple experience. I live in Canada’s Yukon (Think Alaska or Siberia if you don’t know where that is; it’s North and the winter can be very, very, very cold). I have a pair of down mits, whiches are fairly warm untill it gets below -35 Celsius. From that point on, you can just feel the cold air getting through. I’m not talking about having cold hands, I’m taking about feeling the air through the weeks spots of the mits ( just like a sleeping have weeker spots). Anyway, the point here is that if you wear a thin pair of gloves in the mits, you no longer feel that cold air comming through and the mits that were not warm enough are suddenly just fine. I observed the same thing with a full down jackets ( the big ones). It ok with a t-shirt till -40, butbelow that, you really need to layer up under to stay warm. I was wondering why it would be any different with sleeping bags… it seems that it’s not, thank you for confirming that. I don’t know about this theory about the down being activated by warmth, but even if it does, in real life, it’s still warmer with a extra layer under. As mentined in the article, not to tight, and not too much so that there is no more air left in between.

    Maybe some magic happens when you’re sleeping that change the phisics of it all and make sleeping bags behave differetly, but i doubt it.

  4. Philip Broughton-Mills

    I think the origin of this may have been the old rating standards. When I bought a sleeping bag shortly after the millennium, the smallprint stated that the temperature comfort ratings were based on a 20-year-old nude woman. (I remember vividly because I wondered how I could become a sleeping bag rater!)

    Nowadays, sleeping bags use European standard EN13537:2012 (https://en.wikipedia.org/wiki/EN_13537) which classifies a standard woman as age 25 and wearing a baselayer.

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