Steve -
I just re-read your first post, and realized you were talking about keeping your feet warm while snowmobiling, and my reply was oriented to winter hiking. Those two have somewhat different needs to keep your feet warm. As a bit of background - my cold-weather experience comes from living in northern New England until a few years ago when we moved to the eastern Sierra.
The thickness of the vapor barrier is likely to have much less significance when you're snowmobiling, as your foot is mostly immobilized. When you're hiking, you want it as thin and unobtrusive as possible, or it can cause blisters.
What boot do you use snowmobiling? And do you use chemical foot warmers?
