After three weeks sleeping in sub-zero temperatures, we’re getting a warming trend. I had plenty of insulation (2 sleeping bags), so I haven’t been cold at night. I have, however, had to deal with frost. Living and sleeping in subzero temperatures is an exercise in moisture management. The moisture expelled by your skin ends up as frost in the insulation of your sleeping gear, as well as in your boot liners. These must be dried daily, or they soon begin to lose the ability to keep you warm. In temperatures above about 10 degrees F, I’ve never had moisture build up from frost become an issue.
For sleeping bags, this will build up even if you aren’t breathing into your bag (which you shouldn’t do because your moist breath speeds the rate of icing).
As I was busy running a course, I wasn’t always able to get everything dry that I needed to. On two nights there was enough ice buildup in my sleeping bag where it was noticably cold when I got in. It soon warmed up from my body heat, and I took the time to dry it out the next day.
The challenges presented by extended stays in bitter cold must be met with a well-reasoned approach to maintaining the viability of insulation by managing moisture. When this is done well, living out in the cold is a much more enjoyable experience.