Originally Posted by beep
There are few people on the planet with more cold weather trekking/camping/expedition experience than Lonnie Dupre
. Lonnie was a presenter at the Winter Camping Symposium in Minnesota. When I asked him how he dealt with the buildup of frozen moisture in sleeping bags for day after day of travel in severe cold, his answer was (paraphrasing)...use a vapor barrier between sleeper and insulation. In his case, he slept in a single layer of baselayer garment using a vapor barrier "inner bag" separate him from the several inches of down in his sleeping bag. The morning routine involved a quick change into a dry baselayer before layering up for the day.
Vapor barriers can be tricky to manage, but for serious cold they can be a lifesaver.
Exactly right, vapor barriers are key. I have always used down, but can understand the cost factor. I want the person who has slept in a soaked through synthetic bag tell me how "comfortable" that was. Wet is wet, and while synthetic may be better when wet, I would not want to test that out. If enough caution and propper plannig is used wetting a bag out can be avoided, and if you plan properly you will have other methods of surviving.
I am very careful about planning and executing that plan, obviously things do not always go to plan (the best survival tool is between your ears), but thinking you are going to survive a sub zero night because you have a synthetic bag over down (when wet) is just foolish, There is just not a comparison in terms of quality, warmth to weight ratio, and bag life quality down bags such as Western Mountaineering are just better.