I've been using the Blackcomb ECO long sleve half zip and bottoms for about 10 skis so far. I'm 5'8" 165 lbs and ordered mediums which fit perfectly. I've used them as my base layer in temperatures from -5°F to 27°F on skis from 5 - 13 miles and am a profuse sweater. They keep the sweat off my skin, I've never been warmer during skiing.