25

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.)

Community
  • 1
Anko - inactive in protest
  • 1,991
  • 2
  • 18
  • 29
  • 9
    I believe you've confused the claim. This sounds like the (scientifically dubious?) first-aid technique of [body-to-body rewarming](http://outdoors.stackexchange.com/questions/3786/can-body-to-body-rewarming-be-used-as-a-last-resort-treatment-of-hypothermia) 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 Apr 17 '16 at 11:19
  • 1
    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 Apr 18 '16 at 09:59
  • One side of the person will benefit from cloths. So unless all the people can fit in the same cloths, I expect that **dry** cloths should be used. However could a case be made for putting a coat for example over both people? – Ian Ringrose Apr 18 '16 at 13:34
  • @KilianFoth Crawling into a carcass is an old theme in westerns. – gerrit Apr 18 '16 at 16:51
  • 8
    @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 Apr 19 '16 at 02:04
  • @LorenPechtel yes, that's correct. This is what I think the OP has found references to (possibly filtered through real or fictional people's accidental or deliberate misunderstandings). – Dan Getz Apr 19 '16 at 02:10
  • 1
    @DanGetz I'm specifically asking about *preventing* hypothermia here, not *treating* it, though that may indeed be where this stronger claim originally stems from. – Anko - inactive in protest Apr 19 '16 at 02:13
  • @DanGetz Good point--it's probably a misunderstanding by those who haven't studied wilderness survival and are mistaking a special-case approach with a general-case one. – Loren Pechtel Apr 19 '16 at 02:18
  • 2
    @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 Apr 19 '16 at 02:22
  • @jamesqf there are "citations" to that in some of the Nazi experiments, which is horrible on many levels. – tedder42 Apr 22 '16 at 17:42
  • @tedder42: I was thinking of much more pleasant experiences, involving me and persons of the opposite sexual persuasion :-) – jamesqf Apr 23 '16 at 17:33
  • 1
    This claim's based on correct physical reasoning (see SE.Physics in ["Surface Area: Volume and its relation with heat"](https://physics.stackexchange.com/questions/100280/surface-area-volume-and-its-relation-with-heat)), though nudity isn't required so much as beneficial. – Nat Sep 18 '17 at 13:25
  • 1
    @Nat: Nakedness will reduce the amount of exposed surface as some of the heat will be lost through convection of air through the clothes between the bodies. OTOH the loss of extra insulation on the outside will more than offset that benefit. – SF. Sep 18 '17 at 14:44
  • @SF. True, and I think that this is one of those cases where we can construct extreme examples showing that it's technically possible for it to go either way (e.g., it helps if they're both wearing body-wide heat sinks, hurts if they're both already wearing extremely thick clothing). I suspect that part of the strategy isn't so much maintaining max heat so much as distributing it most beneficially; while both people might be cold, the one who'd have been colder benefits more from the one who'd have been warmer. Plus vital spots (e.g. torso) might be help warmer by having them pressed. – Nat Sep 18 '17 at 15:03
  • 6
    @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. Sep 18 '17 at 15:16
  • 1
    Does Paris Hilton declaring the practice to be "very hot" suffice as validation of the claim? – PoloHoleSet Sep 19 '17 at 18:49
  • 1
    One might also experience a higher perception of being warm because you can feel the heat coming off of the other person's body. But, it's like I tell my wife when she complains about being cold and doesn't understand why I say she's warm to curl up to, someone else feeling you're warm means you're losing heat to them. – Sean Duggan Sep 19 '17 at 20:38
  • 1
    @SF. Followed by serious temperature decrease through excessive sweating caused by that physical activity? – Brian Drake Apr 04 '21 at 11:41
  • @BrianDrakethat's why you are supposed to maintain the physical activity until the outside temperature improves (e.g. until sunrise). – Evargalo Jun 23 '23 at 06:59

1 Answers1

6

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.

bukwyrm
  • 1,585
  • 1
  • 20
  • 31