I think spun knitted dog fur are the driest and warmest, but you can more easily obtain Duofold winter briefs from campmor.

oh maybe you didn't mean winter? In dry summer conditions whatever you wear normally are probably ok but take two pair on a long hike. In damp conditions cotton is really bad as when you wear wicking long underwear, ALL of the sweat will be transported into your cotton skivvies and I have removed them with a pair of scissors on my knife.
Jim