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.
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.SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.
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.
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?!
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!
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.
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.
Sleeping in a 0 degree bag on a 35 degree night. I’m surprised you didn’t sweat to death.
I wonder if your clothes compressed the air gaps in a mummy style bag. The thing people don’t always know is that an air barrier is a great insulator, but if you lose the air barrier and you just have each layer touching one another then the cold air is reaching your body by direct contact from one layer of clothing to another. It is the air barrier that keeps us warm. So same thing as in the article. If you have too many clothes to the point that you are compressing the barrier, it would make sense that sleeping with no clothes on in that situation would work better.
I’ve always slept Naked on winter camping trips and have never gotten cold in fact just the opposite I get so warm at time I unzip the bag just to cold down
Living in Minnesota air temp in the middle of winter can dip to -40 overnight
Tried one time in just long underwear and was not comfortable because I was cold
But to each his own
Exactly naked is warmer
The people who get cold don’t have the right bag for the temperature
While I agree with the article, I could be persuaded to sleep naked with your model…
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.
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.
And it doesn’t release heat if you’re wearing clothes? Use your head man! Where do you think the heat goes?
I learned in the Boy Scouts decades ago to sleep in my underwear in cold weather and it works. When I was stationed in South Korea, we were camped out on top of a frozen rice patty with only a 1 inch foam mattress between myself and the ice and I was plenty warm. I also kept my clothes by my feet just so they would not be cold in the morning and got dressed in my bag. It works for me and maybe not for everyone. Just not sure why people are calling everyone liars if they had a different experience.
…and the old wives tale lives on. Of course it’s warmer with clothes on! Plus, who wants body oils, dirt and sweat on the lining of your bag? Duh!
Surely the way a sleeping bag is designed to work is to trap a cocoon of warm air emanating from your body around you. If you wear too many clothes inside your sleeping bag this cannot happen. If you have more than just a base layer and you are cold, you need a warmer sleeping bag.
That’s the way your clothes are designed to work as well – trapping a cocoon of warm air within the fibers of them. The more layers you add, the more insulation – with the sleeping bag being the last layer.
Same logic used in your house with the wall insulation.
I would not argue with your statement that if you need more than just a base layer and are cold that you should get a warmer sleeping bag but if someone finds themselves in such a situation the solution is still to add layers, not remove them.
The analogy falls over a bit, as you are the furnace in the sleeping bag so you’re wrapping the furnace in insulation – the house will stay pretty cold and the insulation of the house won’t be able to actually do the job. Is there a middle ground…………..?
An army buddy gave me a tip – minimal clothes on when you go to bed (enough to be comfortable) but with other clothes easy to hand (trousers pulled down so they can just be pulled up, that sort of thing) – that way you can avoid overheating at first but still have those layers available for when you need them at that 0300/0400 stage where things get very cold.
And we all know, if you get out of your sleeping bag and have no other layers to put on, it’s a miserable time in the cold until you can get the fire going. Better to have layer/s left waiting to be put on when you get out of the bag.
Analogy is good as-is. If you wrap the radiator (person) in so much insulation (clothing) that the insulation in the walls (sleeping bag) become superfluous then you’ve gone too far.
And anyone who says “I learned it in the scouts” needs to consider the circumstances of the specific persons they learned it from. I have a 17yo Eagle Scout and while some of the leaders are good and knowledgeable there’s a greater % that have no idea what they’re talking about. There’s no specific training or background to become a scout leader.
If you sleep naked and stay warm enough, that’s great but you can’t sell me on the idea that if you sleep naked and wake up cold in the middle of the night your first inclination isn’t going to be to throw some layers on.
The best explanation here by far
But the radiator also happens to be the thing you’re trying to keep warm, so wrapping it is good
It easier to stay warm than it is to get warm. It’s important to stay warm. Sleeping naked risks getting cold if air gets in or the sleeping bag is opened. Sleeping in thermal underwear keeps you warm even after you’ve opened the sleeping bag. If you have on thermal underwear (and hat, socks), you have time to add outer layers right away after getting out of the sleeping bag, before getting cold (fleece, snow pants, and heavy coat). I’ve camped down to 0 F.
As an older hiker I invariably have to get up once at least in the night for a pee. If i wasnt partly dressed in the sleeping bag i would have to put on something warm each time
This so called ‘theory’ is not scientific, it is just your opinion and not really correct. You are basing it upon your experience and NOT what happens in reality, everyone’s circumstances are different.
To each their own and you can always add a layer to experiment. I prefer less layers so that the heat I generate lofts the bag and is trapped inside, I am much warmer this way than with many over layers. T shirt and undies is plenty -for me, at 15 degrees in a zero bag.
We’re all different. However, the idea that your bag is a house and you are the furnace is true but to say that you’re warmer in your house with clothes on doesn’t make sense. Your sleeping bag is not 2500 square feet of empty space by any proportion to your “human furnace”. Of course your warmer in clothes in a massive empty house versus being naked. Your furnace isn’t the size of your house unlike your body to bag proportions. And, your down bag is better at trapping heat than a house. Apples to apples please.
P.S. I did like the article and liked the different ideas, suggestions and POV :-)
I remember a military movie where they told each other if you wear your long Johns in your sleeping bag you’d die. I always questioned that. I guess the myth stems from deaths that happened for some of the exceptions that were mentioned in this article, but people didn’t understand it was those specific circumstance that long Johns can be dangerous, rather than in general
Probably from the age when soliders wore cotton long johns.. Wet cotton long johns