I wear the Ibex briefs under my all-purpose tights - mostly so I can wear the tights more than once between washing. No clammy, no chafe, no ride up. I don't think I'd wear underwear under compression tights. I really like all my CW-X legwear, including the Insulator tights which are good down to 35° or so, but they aren't cheap, and I save them for my longest runs and races.