I have only tried it on; I haven''t used it in  cold weather yet.  Size large fits me (5''11", 160 lbs, athletic build), but I misunderstood the fabric.  The polypro is fairly thick for a base layer that''s supposed to wick moisture from the skin.  I hoped it would be more like a single layer, feeling smoother against the skin. The cut around the arm holes is curious, too.  Lifting my arms to shoulder level, and the fabric stretches in the armpits for a mini-flying squirrel look.  I don''t know how this might affect actual use in cold weather with a layer over this hoodie.  During an hour-long cold-weather (35-40 deg F) run outside, I can foresee overheating in this top if there''s a second layer over top of it.