I suppose these guys are the experts and have tested the alternative methods, BUT, I would not want to get everything that I need to rewarm myself to get wet by layering up and then getting in my bag before removing the wet clothes. We had a bud go through the ice on a snowmobile trip, and after we quickly got him out of the water (luckily it was shallow), we stripped him down while everyone donated some clothing, he was rubbed down quickly with a towel, then redressed in less than a minute. His boot packs couldn't be replaced, but they were just dumped out and they rewarmed quickly. We were back to snowmobiling for the rest of the day, and he made no complaints even though it was below zero. Things will certainly change if you are alone or don't have other gear with you.