I use Icebreaker (merino) boxer briefs; I think the weight is their 150. I've used a number of different synthetics (and cottons, though not on trail!), and these merino boxer briefs are by far my favorite. Actually, I've been thinking about buying a half dozen pair for daily home use. They keep me cool when I'm hot, but don't freeze me when the temperature drops. I love the merino in heat! To me, more comfortable than any other underwear I've worn. They manage moisture really well, keeping me dryer (or at least feeling dryer) than most others I've worn. They're comfy! No chafing at all, almost silky. No stink. Personally, I prefer the boxer brief set up, seems to further reduce chafing for me. After a few days (maybe 5?), I've found that if I've been workin' hard that jock itch can be a problem, so I'll sometimes supplement with Gold Bond or baby powder or something…