Originally published (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.
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.
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).
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.