We always wear two-piece suits, although a one-piece would be fine, too. In retrospect -- I think I would have got the single unit. But as for underwear we wore Draggin' Jeans (brand) Kevlar long underwear (shirt and pants) for improved abrasion resistance (should we ever end up sliding along on the salt or pavement). A good upside to the stuff: It is made of a fairly coarse weave material which was very good at wicking the sweat away - and keeping us really, really cool when it was exposed to the air (i.e. no leather suit on). We're the ones you may remember seeing walking around in goofy-looking yellow outfits somewhere near the start line. Goofy - but cool.