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In a bunch of films and other entertainment, when characters find themselves in a cold place with no heating but must sleep, they conclude that to stay warm, they should sleep as close to each other as possible —and naked.

I think it sounds reasonable, until the “and naked” part.

Can reducing clothing help keep you more warm in the sheets with another human?

Or is this just a Hollywood excuse for awkward / intimate encounters?

Significance support: The one example in entertainment that springs to my mind right now is the mention in Big Bang Theory season 3, episode 1 here. I've encountered multiple people independently making this claim, usually backing it up with waffle to the tune of "clothing would insulate you from the other person's warmth" or "having bodies touching reduces their total surface-area to volume ratio, which is warmer".

Related questions: It's definitely not warmer to sleep naked in a sleeping bag, but that's just 1 person. (Also asked on Skeptics SE.)

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    I believe you've confused the claim. This sounds like the (scientifically dubious?) first-aid technique of body-to-body rewarming for hypothermia. This was in the Boy Scout Handbook two printings ago, for example. In the case of hypothermia, any wet (but not dry) clothing is supposed to be removed from the victim, and the idea is that the person doing the warming will transfer more of their warmth if they themselves are naked.
    – Dan Getz
    Commented Apr 17, 2016 at 11:19
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    The latest high-profile instance of this occurs in The Revenant, but that is a different situation: the protagonist slips into the carcass of his horse overnight to keep warm. He undresses only because otherwise he'd have to start the next day in soaked clothes.
    – Kilian Foth
    Commented Apr 18, 2016 at 9:59
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    @DanGetz The intent with rewarming is to help the victim, not to help the group. Overall you lose more heat that way but you transfer heat into the victim faster if you remove the clothing between them. It's a last-resort option assuming the helpers aren't also chilled. If everyone's already cold it's just going to make things worse.
    – Loren Pechtel
    Commented Apr 19, 2016 at 2:04
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    @Anko While I'm no expert I have studied it some as I used to head out into the wilderness a reasonable amount. I've never seen it suggested as a prevention, only as a means of helping a victim. For prevention you keep your clothes but huddle together as much as possible--you will have basically zero heat loss on any part of your body against another person regardless of how much clothing you are wearing.
    – Loren Pechtel
    Commented Apr 19, 2016 at 2:22
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    @Nat: Personally, I suspect the unsaid part of the strategy is to cause serious temperature increase by significantly increasing blood circulation through vigorous physical activity...
    – SF.
    Commented Sep 18, 2017 at 15:16

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No. (If the alternative is sleeping together clothed in the same configuration, from a everybody-at-nominal-temperature starting point)

Your thermal insulation is as good as the sum of it's parts - therefore, if you discard any layers (your clothing), the remaining layers (the sleeping bag) will be less effective than the combination of clothing and sleeping bag was.

If one of the participants has insufficient heat production for the given temperature gradient to the outside the other participants would have to come up with the remainder of the heat. Given that the delta is big, and the heatflow restricted by the double insulation of both participant's clothing between them, there might exist a case where it is actually helpful (thermally) to be naked together inside the sleeping bag.

There is a lot of dynamics going on with human thermoregulation, so if any of the participants feels cold, having the heatflow from another participant might jump-start their own heat production, leading to a more pleasant experience, just like a hot-water bottle does.

My guess is that this claim was extrapolated from the recommended emergency measures for hypothermia, where the goal is to source as much heat as possible from the other participant(s), making it expedient to remove any thermal insulation between them.

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