"It is very difficult to keep a down bag from accumulating perspiration and then freezing."

Wouldn't the same be true of a synthetic bag? (I'm not trying to be a wise guy here. I genuinely don't know the answer; it's been too long since I've used synthetic bags.) I could see that the same amount of perspiration might not have the same effect - the down does collapse when wet; perhaps the synthetic doesn't collapse as badly or as quickly? But certainly, both bags would absorb the moisture?

Also, does the rate of perspiration matter? It would seem that your body heat might drive the moisture out of the bag - I've done that when humidity or condensation has dampened my bag one night; after the next night, it's dry again. However, at -40, with the moisture freezing, the dynamics might be different?

What about clothing? Down clothing would seem to hold moisture just like a sleeping bag.

Would vapor barrier clothing be of any use at those temperatures?

Again, I have no experience with this; my questions are prompted only by what I've read in Colin Fletcher's books (mostly Complete Walker and Secret Worlds.) So, I'll apologize if these sound like stupid questions - Franco and I slugged it out for class honors in stupid.