A common theme that pops up around the campfire is whether it’s warmer to sleep naked in a sleeping bag than to add whatever cloths you’ve got. The debate has just resurfaced on the discussion forums of U.K. climbing, where it started as a question as to whether adding a silk liner to a bag makes it warmer, and progressed into a free-for-all on whether wearing more makes you warmer or colder in your sleepy sack. I figured sleeping bag designers would be the best people to answer this and asked the guys at RAB and Alpkit for their views.
Neil at Rab figures that:
We do not have hard data on this, but would add the statement that a silk liner adds a degree or 2 of warmth to your bag for minimal extra weight; being silk it slides rather than getting twisted round you when you move in your sleep, and as it protects your expensive down bag from becoming grubby it can also avoid an expensive down bag wash (£30) so you cover the cost of the liner by saving on specialist down bag cleaning.
Regarding clothing, I think there is no doubt that wearing thermal underwear or a microfleece type top increases your warmth in the bag. However wearing too much can have a negative effect by compressing the layers of insulation, and even the bag itself, and this is to be avoided. It is all about reducing the amount of air circulation and the number of large air pockets that need to be warmed. One of the best ways to sleep warm is to eat well before you get in the bag! ‘The bag doesn’t warm you, you warm the bag’.
While Nick from Alpkit says:
The debate has a number of conflicting ideas and opinions and so I’ll answer them with a series of statements.
1)If you are at -25….. feel cold and you have the option of wearing a layer of clothing or not ……99 times out of 100 you will chose to wear it.
2)Down works better when its warmed up, so in many cases getting into a bag naked can warm up a bag quicker than if you had clothes on. (so you would feel warmer, quicker) but then it would still be warmer if you had another layer on.
3) Anything that contributes to your thermal resistance (i.e. pretty much all clothing except when its wet) stops heat from your body getting out, so this must keep you warmer. Basic 100 weight fleece is about 0.5 – 1 tog
4) If you wore to much clothing, you might eventually start to compress the down so much …that it’s part in your thermal resistance would be affected and make you colder than if you were naked. (very very unlikely)
In short the idea that you would be warmer at minus -25 in say a -15 Down bag …..naked, rather than with some clothes is a complete load of…..tosh.
Doesn’t seem to get more settled than that, does it?