I would say the -20's is where i call it quits and sometimes i take a little heater with me to sit in this old barn. Don't matter how much clothes you have on or how tough ya are, after -20 you can only sit in the stand so long without having to move. If you keep moving spot and stalking all day it is really not bad at all but i do not think i could ever sit in an unheated stand all day and bowhunt with -20 something bearing down on me.