Like Armada says, this thing is a furnace. It's almost windproof, so together with a nice water/windproof shell they make a truly weatherproof combination. This thing is so silky I make my gf wear it to bed instead of her VS nighty. In fact, I wore it shirtless to 21 Steps on a sub-zero night no problem. If you want to get eye-raped while wrestling bears in -40* this is your armor of choice.