Is it Warmer to Sleep Naked in a Sleeping Bag?

Is it warmer to sleep naked in a sleeping bag?

No. It’s a myth that sleeping naked in a sleeping bag is warmer than wearing 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, it’s your metabolism that 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.

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12 comments

  1. I agree. I’ve heard this myth for a long time. If you think it works, why do you wear layers under your down jacket? It’s exactly the same principal with your sleeping bag. Layering to keep warm is the same no matter how you apply it.

  2. Actually, the myth is: It’s warmer when TWO naked people (that like each other helps) share a sleeping bag. And…it’s no myth?!

  3. This has been pushed since I was a kid (and I’m in my 70s), I tried it back then and it was bull! (with the possible exceptions listed). This fallacy is especially obvious when you have to get up in the morning to get dressed, naked is COLD!

  4. I was told in the 70’s when I was a Boy Scout that you would stay warmer if you slept nearly naked, in dry clothes that is. When I was 15 I slept nearly 100 nights in a row in my backyard. I experimented sleeping nearly naked and with clothes. It was hard for me to know what the temps got down to in the night and if it made a difference or not. Now that I am 61 and have measured the low temps during the night while sleeping outside I have determined exactly what this article said… the more clothes you have on is better. I am an architect and I understand the house being your sleeping bag and if you wear extra clothes you will be warmer. It’s a no brainer….. but I fell for it for many years… I slept in a tent just 3 days ago with sweat pants on and a flannel shirt and goose down coat…. I was warm! Forget naked! Thermodynamics overrules nakedness….lol.

  5. The analogy of a house is BS. Sleeping naked or nearly naked is taught to prevent the excessive use of clothing preventing the body heat from warming the relatively small confines of a sleeping bag. The house analogy Is wrong because a house has too much volume compared the to designed hvac not to mention other means of heat loss.
    And experienced folks leave their clothes for the next day in the bottom of their bag so they to are warm in the morning.

    • Well said. When you isolate too many “heat generating pockets”, it makes for a miserable night in the cold. Using the house analogy, it’s like having an oversized heater vent in 2 rooms and seal the door closed instead of letting the house balance the heat by circulating evenly throughout. Like you said always keep your dry morning clothes in your bag with you (and a spare set outside in a waterproof bag as backup). Not doing so, is a rookie mistake you’ll only make once.

  6. I slept in a mummy bag style 0 deg F sleeping bag on two nights that got down to 35 deg in the morning. I was much warmer naked than with clothes. When experiments contradict theory, revise the theory.

  7. While I agree with the article, I could be persuaded to sleep naked with your model…

  8. When you sleep naked in a bag, your body heat warms the air inside the bag and reduces ‘cold spots’ that you find when you move. Less clothes reduces the sweat held against your body by letting it evaporate. It’s also important to put an insulating layer under your bag and keep your clothes inside the bag to keep them warm. Get dressed inside the bag.
    And of course, sharing body heat with another person increases the effect.
    I grew up camping, I know this from experience.

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