It's warm. Running around in the forest at -6 degrees with only a thin merino undershirt made me sweat. It didn't help even if all the hatches were open in the jacket. I guess we should wait for those -20 degrees below zero, but where can we get them here in the capital region? So I haven't even been able to try it in really cold weather yet.
Just to be sure, you don't want to pack a jacket in your backpack when it doesn't compress well.