I think the depends heavily on having a room/blanket/sleeping-bag arrangement that doesn't leak a lot of heat. In extremely cold, drafty situations (living in

I think the depends heavily on having a room/blanket/sleeping-bag arrangement that doesn't leak a lot of heat. In extremely cold, drafty situations (living in unheated bus) with only blankets rather than a sleeping bag, putting on clothes is necessary. Of course, if you have a good sleeping bag, as little clothes as possible is how to sleep outdoor.