Being in the Army, and recently stationed in Korea, where it gets COLD!!!, I was issued some Bates Extreme cold Weather boots, that were a Goretex, black leather boot, that came with 2 pairs of insulated booties for the boot. When you kept those clean and dry, your feet stayed warm as well!!! They kept my feet warm in temperatures down to 38 below zero( counting windchill)!! Now for CO, I have a pair of Irish Setter Big Game trackers with 800grams thinsulate. They seem to do a good job of keeping my feet warm. The most important thing is to keep your feet dry!!! take extra socks and change your socks if your feet start to sweat!!!!