A few years ago I was camping in the Negev in southern Israel. Since its a desert, there is no surprise that weather changes consistently during day and night. I was camping with some friends and noticed that some of them were taking most of the clothes off before going to sleep. I was asking them why they do so, and they answered: “It is warmer to sleep that way in sleeping bags.” For a quite long time, ever since, I’ve been asking myself – is it warmer to sleep naked in a sleeping bag? A few years of experience and some in-depth readings on the matter brought up some answers.
It is NOT warmer to sleeping naked in your sleeping bag since clothes provide thermal insulation by trapping warm air close to your body.
To support my point, I will present you with the expert’s opinion; the PHD and expertvillage. Sleeping with damp clothing or with too many layers might mislead into thinking that I am wrong – I will elaborate on the topic later on.
A Few Insulation Facts
To convince you that sleeping with clothes on is warmer than naked, I will try the scientific approach. The critical factor in the equation is thermal conduction.
The physics behind it talks about particle collisions, including electrons within atoms. I will try to keep it simple – thermal conduction is merely the process of heat transfer from a hot material to a colder one.
Within your sleeping bag – the high-temperature object is your own body, and the cold one is the environment outside the bag.
In this process, heat goes off your body through the air, which acts as a conductive. If you can trap the temperature within the conductive, you will be able to maintain heat.
Well, that is precisely what sleeping bags do – their insulation contains small air-pocket which trap the air from moving forward.
When you add extra layers of clothing, you add more means that would catch hot air from escaping.
Now, here is the trick – if the air had already passed through your clothes, it would also be more difficult for it to return to your body. For that, in some cases, sleeping with clothes on may seem colder than with clothes off.
However, you should keep in mind that it’s mainly due to inappropriate clothing picking. Instead of cheap clothes, you better keep yourself warm with some cotton or down-filled clothing.
The PHD Recommendations
For those of you who are not familiar with PHD (Peter Hutchinson Designs) – it’s a regional business in the UK which is specialized in extreme warmth and extreme lightness in mountaineering conditions.
I’ve been following these guys for quite a long time now, and they have gained my trust over time. Regarding sleeping bags and thermal techniques; there is no doubt they are among the best.
To our topic, allow me to quote the experts: “Clothing is the most efficient weight-saver in Sleep Systems. Use the warmth of your down clothing to sleep in and you can really cut down the weight and bulk of your main bag.”
The guys from PHD emphasize that sleeping with clothes on increases warmth while maintaining lightweight carry since you merely sleep in your hiking clothing.
I will mention that their arguments aren’t arbitrary – they do base them on case studies which are presented in the previous link.
The Expertvillage Opinion
One Youtube channel which kept me hooked dozens of times is ‘expertvillage.’
With over three million subscribers, there is no question these guys are trustworthy. I’ve gained a lot of my knowledge through their advice and implemented it within many of my journeys.
The advice that I’ll show comes from Richard Fields, which ‘has been an avid backpacker and backcountry guide for over 25 years’.
He says that the first two steps to keep you warm is zipping your sleeping bag all the way and to get yourself a proper sleeping pad for ground isolation.
Besides that, he mentions that his recommendation is to sleep with a long top and bottom cotton underwear to keep you warm.
Take The Socks Example
I believe that one of the most convincing examples is wearing socks since we’ve all experienced how cold our feet could get in cold conditions.
So what is the first thing we all do in this situation? Well, of course, we immediately wear a pair of socks.
The reasons socks keep your feet warm better than sleeping bags is because socks wrap around your feet from all sides. In opposed to that, sleeping bags usually feature a gap between your feet and the inner walls.
The more significant the space, the more heat can transfer through the air – just as explained above. Well, socks create just what clothing do – an additional barrier to trap hot air.
Some believe that socks do poorly concerning thermal conduction since they block blood flow to the periphery. My medical studies, however, showed differently – you need much more severe means to do so.
Confounders: Sweats & Damp Clothing
I believe that many people think that it is better to sleep naked in a sleeping bag since they had a bad experience with clothes.
Nevertheless, I do suggest you take some means to avoid confounders. The first I will be talking about is night sweats.
The reason you tend to sweat with clothes on proves my point, although it could also be the reason why you are getting cold during your sleep.
When sleeping bags get damp, especially when down-filled, they lose their ability to insulate. That is another perfect example in which clothes get you warmer – however in an exaggerated, ambiguous way.
Sleeping bags also get wet when you get in them with damp clothing.
Hiking in lousy weather conditions gets your clothes wet no matter how hard you are trying to avoid it. If you get in your sleeping bag wet – you are going to get cold during nighttime.
Another point to consider is low tents breathability. If your tent doesn’t feature vents and air circulation – condensation will cover your sleeping bag even when your wet gear is aside from you.
Will Adding More Clothes Increase Warmth?
Not necessarily. From my experience, clothes have increased warmth to a certain level and from there – adding more hardly made any difference.
I believe that there are two main reasons for that. First, getting yourself too warm eventually make you sweat and once you do – you soak your sleeping bag and get cold.
Second, you should keep in mind that the source for the warmth is your own body. Once you were able to trap air with one layer, adding more wouldn’t catch any more of it – the gap between your body and the inner parts remains the same.
My final thoughts on that matter are that you should sleep with clothes on, however, for your good – you shouldn’t sleep with too many layers.
When is it Okay to Sleep Naked?
Yes, I do favor sleeping with clothes on – I wouldn’t play with hypothermia. Nevertheless, my experience taught me that there are some cases in which sleeping naked is also okay.
I would let myself sleep with clothes off once the sleeping bag is high-quality and down-filled, for example.
I do trust down-filled sleeping bags more than synthetic even though they perform worse under wet conditions.
I would also feel more comfortable to go naked when sleeping with a sleeping bag liner. Countless journeys had taught me how essential liners could be and how well they perform in keeping you warm.
That would be primarily because they can keep your sleeping bag dry even when you sweat.
Beside the two, I also find sleeping naked essential when sleeping on solid ice. In this scenario, cold gets through mainly from the bottom, so sleeping ON your clothing is better than IN them.
Nevertheless, ice and snow aren’t things to play with, and you do have to consider a high-quality sleeping bag.
Down-filled vs. Synthetics
Another familiar debate is about the best type of sleeping bags, regarding down-filled versus synthetic ones.
Well, down-filled sleeping bags do a great job in keeping you warm since they are filled with the soft feathers poultry maintain warmth with.
These are usually more lightweight than synthetics, which are typically made of polyester.
Both perform worse under wet conditions, however, as I’ve already mentioned – down-filled are affected more.
When having to decide between the two, I would personally favor the down-filled ones, although they are usually more expensive.
From personal experience, the combination of a down-filled sleeping bag and a cotton liner works best even with clothes off.
What is a Good Way to Stay Warm During Nighttime?
The long-lasting debate regarding sleeping with clothes on or off in a sleeping bag is because nights could get cold when camping.
Besides clothing, there are additional means that could keep you warm in your tent.
My first way to go is building a campfire which would burn all night. For a first-time camper it might sound challenging; however, the guide I’ve written and just linked to is quite plane-simple.
The one warning on that matter, which I’ve unfortunately learned from experience, is not to build the campfire too close to your tent. There are many reasons why camping may not be safe, and there is no doubt that is one of them.
Another conventional technique is using ovens; however those I haven’t personally tried, so it’s hard for me to recommend. I will mention that you shouldn’t use the oven inside your tent since it produces CO – which is very toxic.
What Happens to Body Temperature During Sleep?
During the research on the sleeping naked topic, I’ve come across some interesting comment.
One guy said that after he woke up due to cold, he got out of his sleeping bag and took all the clothes off. Then, got in it again and fell asleep again, this time feeling warm and comfy.
That got me into thinking – what happens to our body once we fall asleep?
Experts say that during nighttime our body temperature drops in about two degrees. Also, during some parts of our sleep, the breathing slows down.
When we breathe we exhale water and lose HEAT, so when we breathe slower – temperature drops less, and we maintain warmer.
Combine the dropping temperature with a slower breath, and you get why this guy felt better after taking his clothes off.
Perhaps that wasn’t because he increased thermal insulation, but because he has JUST GOT out of his sleep.
Once you wake up, it takes time for your body to get into awakening physiological status. There is a good chance that his body was still demanding lower temperatures as it did while sleeping.
It is warmer to sleep with clothes on, however, to get sufficient insulation you should make sure you do it right.
You shouldn’t wear too many layers that might get you sweaty, or otherwise – get into your sleeping bag with damp clothing you’ve just hiked with.
Clothes keep your body warm by creating a barrier that warm air isn’t able to pass. The physics behind that is leaning on thermal conduction, which is the heat transfer from a hot object to a colder one.
Wearing more layers do get you warmer until a certain point in which adding more would compromise thermal insulation – the air was trapped and more layers won’t trap it better than it already is.
Instead of wearing too many layers, you can get yourself warmer during nighttime by building a campfire which would burn all-night long.
This way you lower the chances that your sleeping bag soak sweat which would compromise its insulation capabilities, especially with down-filled ones.
There are scenarios in which sleeping naked would still make sense – like when having a high-quality sleeping bag and a sleeping liner.
When sleeping on solid ice – putting clothes underneath would be better than on, although combining the two might work as well.
I hoped I was able to convince you that sleeping naked doesn’t keep you warmer in your sleeping bag. If you have any hesitations or ideas regarding that topic – let me know all about it by leaving a comment below!