Not to argue, and whatever works for you, but when I was in the Army, my first duty station was Fort Drum, NY. I was in a light infantry unit, and we did a lot cold weather training and field time. I was taught as part of the cold weather training to get in your sleeping back in only your skivvies, or at most just your base layers. The idea being, if you climb into a well insulated sleeping bag fulling clothed, or clothed in insulating layers, it increases the chances of you sweating, which then can actually be really dangerous in extremely cold weather. We spent a lot of nights in the field in -20 to -30 temps, and I followed that advice and it seemed to work. I remember a new LT that didnt heed that advice and about died of hypothermia, in his sleeping bag, full polypros, insulating layers, full gore-tex, etc.