Originally posted (in Dutch) on the Dutch Bushcraft Forum on July 22, 2011.
Last week in the Belgian Ardennes I had a discussion with a friend about the effects of wearing clothes when sleeping in a sleeping bag. She claimed that you would be warmer without wearing clothes. Her reasoning had to do with warming up the sleeping bag but I didn’t really understand her.
I disagreed because I suspect clothes help to insulate your body and therefore should reduce heat loss. (Here I assume that the clothing is dry and does not take up that much volume as to compress the sleeping bag and make it less effective). Later at home, for fun, I decided tot test it.
Testing Method
For this test I used my REI down sleeping bag (rated to about 0 C), three 1-liter Nalgene water bottles and my merino wool shirt (Woolpower, 200 g). I filled the three bottles each with 1 liter of hot water from the tap, temp. 59 C (measured with an electronic thermometer, see picture below).
Then I wrapped the first bottle in my merino wool shirt (see two pictures below) and put it in my sleeping bag on my balcony.
I put the second bottle in my sleeping bag without wrapping clothes around it. I placed the third bottle on top of the sleeping bag and this was my control condition. I created different compartments in my sleeping bag with rope to minimise heat transfer beween the bottles (see picture below).
Six hours later, I measured the temperature of the water in the bottles.
Results
|
Bottle |
Temp. start |
Temp. after 6 hours |
| Outside sleeping bag | 59 C | 29 C |
| In sleeping bag | 59 C | 37 C |
| In clothing in sleeping bag | 59 C | 40 C |
The average outside temperature was about 16 C during the test. (I performed the test three times with similar results – i.e. every time the bottle with clothing inside the sleeping bag remained the warmest, then the bottle without clothing in the sleeping bag and finally the bottle on top of the sleeping bag).
Conclusion
The bottle that was wrapped in clothing inside the sleeping bag lost less heat than the bottle without clothing in the sleeping bag. You will therefore likely be warmer in your sleeping bag wearing clothes than without wearing clothes. Like I mentioned before, here I assume that the clothing is dry (and that you’re not going to sweat because of the clothes) and that the clothes are not compressing the sleeping bag making it less effective.
Let me know what your experiences are with wearing clothing in your sleeping bag.
Hey Marc,
Had some purdy cold nights out in the Lake District this spring.
One night, when I was in my sleeping bag wearing nothing but a boxer short, I started getting to cold. When I threw on a fleece, I was more comfortable once I shivered myself back to warmth.
Adding an extra insulating layer of clothing is the logical thing to do to stop convection and with that heat loss. It’s not about warming up your bag like your friend suggested, it’s about trapping your body heat as close to your body and as effectively as possible so far as I can tell.
Love the blog, mate!
churr
There is a logic to the “warm up the sleeping bag” theory, but it applies more to mountaineering in very cold conditions. The theory is that if you are already cold and your clothes are cold you don’t want to just get right into the bag as you are (something a climber might do) – in this case the insulation will serve to keep you cold for longer. It may be better to place these clothes on the top of the bag and warm up before you try to sleep. The clothing may also reduce your circulation in a close fitting bag (which is more efficient anyway). You could test this by putting iced water in the bottles and see which one takes the longest to melt/warm up.
Dear Sirs, regards from Finland!
The statement, that reducing clothing in sleeping bag would keep one’s body warmer is pretty surprising!
That would be the only known case in physics in which decreasing the thermal insulative material would increase the thermal insulation!
For Mr. JB: In the scenario You described You must simply jog, made push-ups or wrestle with Your comrades to warm up Your body before entering into Your sleeping bag. Now Your body and clothing are warm, but it is very important to avoid sweating and any moisture in the clothing.
Our body is losing about 30% of heat via our head. Therefore in cold conditions a good, woolen balaclava is very good in sleeping bag – as well as thick woolen socks!