This jacket is very warm, I use it at resorts only because hiking in it would be like taking a saline shower. Too warm for anything above 21 deg F. The best warmth for temps around 10 deg F. w/ one light layer, as long as your turnin hard. Fits a little big, I'm 5'10" 165lbs and a medium fit good except my shoulders were tight and the arm length was short. I traded for a large now its a little long and baggy but my shoulders love it and my sleeves dont pull up when I bend over to strap in. The pit zips are weak little zippers and always get stuck on the inside flap. It gets really bad when the zipper gets stuck and your ridding the chair back up in 0 deg F. But after a while I learned how to be very careful with them. I'm not sold on the riri zipper either because it can freeze lock. for instance, if is freezing up top on the MT and below freezing at the base, then geting back up top will freeze lock the riri zip. The jacket is sweet but it only gets 4 stars for the zips.