One myth that I constantly hear is that it is warmer to sleep naked in a sleeping bag than in pajamas. Here’s the definitive answer and why – in some situations – sleeping naked might actually feel warmer.
Quick Answer:
Sleeping naked in a sleeping bag is not warmer. The more insulation you have on your body, the warmer you will be. The main exception to this rule is if you are wearing cotton pajamas and they get wet, such as from sweat. Being wet makes you feel cold from evaporative heat loss. In this case, it might be warmer to sleep naked.
Sleeping in Clothes Is Warmer
As logic would dictate, wearing clothes in a sleeping bag will make you warmer. The more clothes you have on your body, the more your body will be able to trap heat.
In cold weather, campers and backpackers often wear thick pajamas or their puffy jackets to stay warm at night. This isn’t as effective as using a sleeping bag which is truly rated for cold temperatures, but good pajamas can add a few degrees of warmth to your sleeping bags without having to buy a warmer bag.
Also read: Pro tips for camping in snow and cold weather
But Sleeping Naked Is Warmer than Sleeping in Wet Clothing
There is one main situation where sleeping naked in a sleeping bag might actually be warmer. This is if you are wearing cotton clothing and it gets wet.
When cotton gets wet, its fibers compress and sit directly against your skin. Cotton won’t provide any insulation when wet. Even worse, your body heat will cause the water in the cotton to evaporate, which results in evaporative heat loss. This is why backpackers often say “cotton kills.”
It doesn’t take a lot of moisture to make you feel cold. This is why you should always have a dedicated pair of pajamas to wear camping. Do not wear the same clothes you wore during the day as pajamas, since they are probably slightly damp from sweat.
Other Situations Where Sleeping Naked Might Be Warmer
- You are wearing so many clothes that your sleeping bag insulation ends up getting compressed
- Your clothes are very tight and restrict blood flow
Also read: Is it okay to wear cotton when hiking?
The Layering Principle Applies to Sleeping Too
You will need to follow the layering principle when sleeping in a tent too. No, you don’t wear three layers to sleep!
Rather…
- Pajamas = base layer
- Sleeping bag = mid layer
- Tent = shell layer
Remember that the main purpose of the base layer is not to keep your warm. Instead, it is supposed to wick sweat and moisture away from your body.
The mid layer, also called the insulation layer, is what actually keeps you warm. And the shell layer keeps you warm by protecting you from wind and moisture.
Pajama Material Matters
We’ve established that your pajamas are the base layer of your sleep setup. And, just like with hiking base layers, material matters.
You need to choose pajamas which will wick moisture away from your body. Synthetics are great for this. Merino wool pajamas are also great because they are comfortable to sleep in and provide some insulation as well, even when wet.
If you must wear cotton pajamas when camping…
Make sure you don’t overheat and start sweating. Don’t zip your sleeping bag up right away. Instead, wait several minutes to let your body adjust. If you still feel cold, partially zip up the sleeping bag and wait a few more minutes.
On cold nights, it’s hard to have the willpower not to zip up right away though. That’s why it’s better to just invest in some good pajamas.
Also read:
Where Did the Sleeping Naked Myth Come From?
The myth that it’s warmer to sleep naked when camping has been around for a long time. I found a reference to it in an old issue of Outside magazine from 1996, but apparently a lot of people were told this in the Scouts long before this.
My guess is that this myth was started by a guy who was camping with a female friend. 😉 But the myth seems to have originated with a misunderstanding of how sleeping bags keep you warm.
Many were mistakenly told that, “The warmth of your body will create a microenvironment of very warm air right next to your skin…and there is no way you will get that warm if clothes block contact with the air.” Obviously this isn’t true since wearing clothing will only add to the amount of heat trapped around your body.
The myth might also come from a misunderstanding about how to treat hypothermia. If a person is hypothermic, you are supposed to remove their wet clothing and put them in a hypothermic wrap.
As an old Princeton article on hypothermia points out, you do not put them naked in a sleeping bag with another person: “No matter how cold, patients can still internally rewarm themselves much more efficiently than any external rewarming.”
Sources:
https://physics.stackexchange.com/questions/18484/could-a-sleeping-bag-be-warmer-if-you-are-naked-inside,
https://bushcraftusa.com/forum/threads/do-you-sleep-naked.125797/page-2,
https://www.hammockforums.net/forum/showthread.php/7994-Sleeping-naked-is-warmer/page10,
image credit: “Grady Slept in My Van” (CC BY-NC 2.0) by nep
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