Nakey Time! Well, maybe not.
December 2, 2010 5:20 PM   Subscribe

Is it warmer to sleep with pajamas or naked?

I have always heard that sleeping naked keeps you warmer than wearing clothes. I have experienced this, and a few people in this previous question seem to concur with that premise. However, I tried to explain this to my husband, who says that makes no sense. My explanation involved me saying, "the heat goes in circles!" but I'm hoping to get a more science-based answer.

a) Have you experienced this phenomenon and b) do you have a reasonable explanation for it?

Also, does it make a difference if there's two people? I always overheat sleeping with the hubs, but the effect is less noticeable when we wear clothes.
posted by emkelley to Grab Bag (27 answers total) 4 users marked this as a favorite
Maybe it depends on the clothes. All of my PJs are cotton or fleece and, well, I wear them because otherwise I would be cold.
posted by SMPA at 5:25 PM on December 2, 2010

Pajamas are definitely warmer. I usually go without, but on the few really cold nights before my building turns the heat on, I find that pajamas are necessary. (If I sleep naked on those nights, I'll wake up in the middle of the night from the cold.)
posted by ocherdraco at 5:27 PM on December 2, 2010

Theory: Different types of materials will conduct heat at different rates, and blankets and PJs are generally not made of the same materials. Moreover, people will have wildly different types of materials. Some people need to sleep with their PJs because they have a crappy blanket. Others can sleep without PJs and be warm because they have good blankets.

Moreover, other scenarios can be true -- you can be in PJs and be cold because both the PJs and the blanket are wicking away heat. You can be naked and be overheating because your blanket/sheet combo is particularly great at holding in heated air and trapping it near your body.

And then there's the tactile element. You may feel warm (or cold) simply because more of your bare skin is touching a particular type of fabric that just feels like it should be warm or cold.

You'll never get a good answer, because there's so much variance at work here.
posted by Cool Papa Bell at 5:34 PM on December 2, 2010 [1 favorite]

I would guess from my own (totally subjective) experience: sleeping in clothes traps the heat closer to your body when sleeping, insulating you from heat escaping but also insulating your partner against your heat (and vice versa). When you sleep naked alone your body heat has a greater space to heat (instead of heating against the close pajamas, it has to fill the volume of the entire under-the-blanket area). When you sleep naked together you combine your body heat underneath the sheets and so probably it feels hotter.
posted by johnnybeggs at 5:34 PM on December 2, 2010

If I could ensure that I would remain completely ensconced by by blankets all night long, I wouldn't have to wear clothes to bed in the winter. But there's always some bit that pokes out, whether it be my butt when I turn over, a leg when the blanket gets pulled the other way, or an arm to prop the pillow when sleeping on my stomach. For that reason, winter requires me to wear long sleeves and socks to bed at the very least, and leggings on especially cold nights.

For me, it's absolutely not the case that being naked makes me warmer. If you want to run a controlled experiment, try sleeping with one naked foot and one foot in a wool sock. See which one is warmer.
posted by phunniemee at 5:36 PM on December 2, 2010

I generally sleep naked. When it's cold I'll sometimes throw a shirt and some fleece pants on and it never fails to make me feel warmer through the night. I can't think of a single reason that sleeping naked would be warmer, even with two people (you might feel the warmth of the other person faster, but it's still going to be easier for it all to escape).

I'm pretty sure this is a combination of psychosomatic effect and old wive's tale.
posted by 256 at 5:37 PM on December 2, 2010

To treat hypothermia outdoors, two naked people buddy up in a sleeping bag. So I'm on team naked.

Of course, getting out of bed in the morning is less fun.
posted by charmcityblues at 5:38 PM on December 2, 2010 [1 favorite]

A good principle of heat is making a layer of warm air trapped.
PJ's plus bedding = more layers of trapped air being warmed by your body.

Just put a temperature gauge against your skin and take samples with PJ's on and with PJ's off.

The only way I could think of a cotton PJ making one cooler is if they get so hot that they sweat which will cause rapid evaporation cooling from being wet.

Two people touching will create a larger sensation of warmth. Think of it like two combined BTU heaters instead of two separate ones being covered in layers. It will heat up the air under the bed quicker.
posted by zephyr_words at 5:40 PM on December 2, 2010

Scientifically, I'm sure that the more insulation you wrap around yourself, the warmer you will be. However we don't have thermometers on our skins, and our perception of heat depends on a lot of other things. In my case I found that for overall comfort, freshly washed flannel pajamas are the best. I think because pajamas I've worn before have various skin oils and dried sweat and who knows what else.
posted by phliar at 5:43 PM on December 2, 2010

I have never heard of this and always throw on clothes when it's cold out, along with extra blankets. More layers keep you warmer.
posted by nomadicink at 5:44 PM on December 2, 2010

Loose clothing is strictly warmer. It's the air that acts as insulation (scientific term I think is specific heat), and the clothes keep it close by and prevent it from circulating. The reason you get naked in hypothermia is to eliminate those insulating effects. If you wear tight clothing, there's no warm air to trap.

There is a point though, where warmer is worse. If you begin sweating because you're too hot, at least for me, it goes overboard and you wake up quite cold yet sweaty.
posted by pwnguin at 5:45 PM on December 2, 2010

zephyr_words: "Just put a temperature gauge against your skin and take samples with PJ's on and with PJ's off."

The problem with this idea is that you are warm blooded. Your body will react to this by spending energy.
posted by pwnguin at 5:47 PM on December 2, 2010

I suspect the cause for the mistake (and I'm pretty sure it's a mistake) is the second part of your question. If it's warmer with the husband when you're both naked than when you're both clothed, then therefore it's warmer naked, right?


On your own, you're producing a certain amount of heat, and wearing PJs will keep a layer of that heat close to your body. When you're with the husband, however, you're (literally) up against a perfectly shaped heat generator with a whole lot of surface area, which is great for transferring heat to you. If he wears PJs, that will reduce the amount of heat that gets transferred to you, which will (understandably) lead to the conclusion that it's warmer without PJs on.
posted by twirlypen at 6:02 PM on December 2, 2010 [3 favorites]

If you wear tight clothing, there's no warm air to trap.

Not so. Thermal long underwear is designed to be worn tight and to trap a thin layer of warm air within the material next to your skin. This is also how body hair works.

I always overheat sleeping with the hubs, but the effect is less noticeable when we wear clothes.

Indeed. The clothing acts as insulation between you two. If your observations are based mostly on sleeping in pairs, then this will be a big factor.
posted by ssg at 6:03 PM on December 2, 2010

I notice that my feet are colder if I wear socks to bed. While I generally agree that having clothes to trap a thin layer of air near your body is warmer, if the clothes are snug enough to restrict any of your circulation they might make you feel colder. That's my theory to explain the sock effect.
posted by vytae at 6:14 PM on December 2, 2010

Naked, or close to it. The thing is, if you wear PJs and keep the heat all close to you, you warm up and your body shuts down to keep from overheating but the rest of the air under the blankets in your bodyspace and the bed and the surface of the blankets stays cool. If you're naked you burn a bit more energy but you heat up the whole of the bodyspace and surfaces of the bed and blankets so the whole area you move around and toss and turn in is all warm! And there's a lot more warm air to hold the heat. In PJs you end up in a cold bed all around with a thin layer of warm air that quickly goes away when you roll over into a cold spot. You can't warm up the bed if you're being all miserly and trying to keep all the heat right next to your body trapped in your PJs.
posted by zengargoyle at 6:24 PM on December 2, 2010

Sometimes I get too hot and sweaty with my skin against my (and/or my wife's) skin. Under those circumstances it is less uncomfortably hot for me to put on light pajamas: to buffer my skin against heating up other parts of my skin, and to absorb a bit of any sweat that I might produce and keep that from getting gross & sticky.
posted by xueexueg at 6:46 PM on December 2, 2010 [1 favorite]

re: charmcityblues - I think the goal is to heat the cold person up as fast as possible - so both people are naked to reduce the insulation between them, not because it makes both people warmer.

Also, seconding the circulation issue - any clothes that restrict circulation will make you colder. Tight rock climbing shoes are a notorious example of this.

I'm with zengargoyle though - but only if you have really insulating blankets. This is true in my nice winter sleeping bag when it's not actually that cold out, but not at all true in my crappy summer bag. I guess it's a trade-off between the rate you produce heat and the rate of loss through the blankets.
posted by lab.beetle at 6:46 PM on December 2, 2010

That's my theory to explain the sock effect.

My sock theory is that my feet sweat, a litte. So while I don't notice my feet or socks being sweaty, they're subtly damper [and thus colder] than my feet are without socks. If I put on brand new dry socks right before bed, my feet tend to stay wamest. But naked feet are warmer than if I get into bed with the socks I already had on. I assume the same thing is true with other clothes. If they're at all dampish or cold to start with [esp cotton, less so with wool and other special fibers] you'll use up energy warming them up. Otherwise jammas are warmer.
posted by jessamyn at 7:08 PM on December 2, 2010

There has long been a faction at my summer camp (which is pretty far up north, so we end up camping in some damn cool weather) that insists that naked in your sleeping bag is warmer in your sleeping bag. This cannot be, since the more insulation you have, the more heat you'll retain.

However, I have developed an explanation for why my otherwise intelligent friends would believe such an outrageous thing. If you sleep naked, you'll warm up more quickly. Sleeping bags (at least - this may hold true for blankets as well) are made out of materials that "reflect" heat back onto your body. So if there is no clothing between your body and the material of the bag, your body heat is immediately "reflected" back onto you, you feel that, and you perceive yourself to be warmer, faster. If you wear clothes, they keep your body heat closer to you for longer, and your bag doesn't do the insulating until enough heat seeps through your clothes to let its reflective properties go to work. If you fall asleep before that happens, you'll never feel that "toasty" feeling that come from bundling up in a sleeping bag. But if it gets really cold, you'll wish you had your clothes on, since the bag isn't impermeable, and your body heat is going to slowly seep out. Clothes slow down that process, and increase your long-term warmth. To the extent that blankets also "reflect" body heat, the same effect will occur.

I think.
posted by PhatLobley at 7:44 PM on December 2, 2010

For me, my perception of warmth is based on the warmth of my feet: cold feet = cold body.

Because of this, wearing PJ's holds in the heat
and doesn't allow it to warm my feet.
posted by 47triple2 at 8:09 PM on December 2, 2010

In the summer my husband and I both sleep naked; in the winter we wear our silk or merino long underwear. So, in both of our experiences, pajamas are warmer than naked. When it's cold out, I'm much more comfortable with a PJ-equivalent on.
posted by Lexica at 9:02 PM on December 2, 2010

> To treat hypothermia outdoors, two naked people buddy up in a sleeping bag.
I thought that that was just so they'd share body heat. It's no use putting just one person suffering from hypothermia naked in that sleeping bag
posted by Neekee at 10:44 PM on December 2, 2010

Like PhatLobley, I have an intelligent, outdoorsy friend who insists that you'll be warmer naked in a sleeping bag than dressed, and have long scratched my head at the whole thing.

The only reasoning for it that I can fathom is that you'll at least warm up more evenly if you're sleeping naked. I tend to get really cold feet when I'm camping and so pull on thick socks, but I can see how it might be better to let the warmth generated by your torso circulate throughout the sleeping bag to warm you all over, rather than having lots of little pockets of air trapped up and down your body by waistband/sock cuffs etc. But whenever I've tried it I just end up feeling cold all over. Now I just take a hot water bottle camping :)
posted by penguin pie at 12:36 AM on December 3, 2010 [1 favorite]

Wearing more clothing certainly makes you warmer. The myth that you're warmer naked in a sleeping bag is total bunk. I've spent nights outdoors at ~5 degrees F in the Whites and can personally assure you that I was wearing everything I had with me and was not cold, but still certainly not warm. I one led a trip with a pro-naked sleeper who assured us that he would be toasty in his 0 degree bag just in his skivvies, but he was up and piling on clothes after about 15 minutes shivering in his bad.
posted by Aizkolari at 5:09 AM on December 3, 2010

I think the whole "naked is warmer" thing comes from all the stories in Scouts, nature shows, etc. about hypothermia. If someone is hypothermic, you're supposed to take their clothes off and get in a sleeping bag with them naked since your body heat will transfer to them much more quickly.

But if it's just you sleeping, the more clothes you have, the warmer you'll be.
posted by venividivici at 7:02 AM on December 3, 2010

It's not as clear cut as people are making it seem. If you had an electric heating element, and you wanted to maintain a steady temperature, higher than the ambient temperature, in a small area, then the more insulation you have the less energy you will have to run through your heating element to maintain the temperature. This, however, has very little to do with the actual question. The perception of cold is not directly correlated to the amount of energy required to keep your body at 98.6 degrees. Instead it is about relative temperatures. It is certainty possible that for some people, sleeping naked feels warmer. Possibly because more of the blankets are heated up, so when you move you don't get cold.

If we are talking about wilderness survival, yes, you want as much insulation as possible. If you're sleeping in your bed, your subjective experience of warmth is more complicated.
posted by Nothing at 7:22 AM on December 3, 2010

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