I took a 4 day trip to Quebec in the heart of winter. Temperatures reached -30 easily. I used this fleece as part of my layering. I had a smartwool baselayer, this fleece, an atom LT jacket, and then a shell. The core of my body stayed amazingly warm! I would shed layers when I went inside, but I'd always leave this fleece on. It breathes well and doesn't need to be taken off in warmer locations.I purchased a small (5'11", 155, 30w) and it's a rather perfect fit. It's cut trim, in my opinion, so it's perfect for going over a shirt or two that you may be wearing.