In reply to deepsoup:
"Viloft is made from wood pulp which increases thermal performance."
Another good one. It's just cellulose acetate, aka Rayon, aka Viscose, aka Modal aka...
http://en.wikipedia.org/wiki/Rayon
Having said that, I like the North Cape RhovylTherm base layers I've got, for cold weather use. And they're a similar mix of Modal (cellulose acetate) and polyester. They're probably about the same weight as these, and warm. But they do hang on to sweat; not surprisingly, since it's quite a thick fabric.