I have Rocky 1200 thinsulate boots and after about 4 hrs, if its around zero degrees my feet start to get cold, a guy at my work told me to try the mickey mouse boots,there army surplus insulatedrubber boots good for -20,i got themand iwear one pair of wool socks, and these boots are awesome,my Rocky's dont even compare,even with two pair of socks,My only reget is i would have been told about them sooner.. there a little heavy,but it worth it.there on ebay or at a military surpus store,that were i got mine cause i never tryed them before,mine was $59.00 new old stock.and i would buy another pair if need be.the ones with the air valve are the newer model,it dont do nothin,keep it closed, its if you go airborne,,they stoped using these boots in 1985 due to cost,best boot for cold weatherfeet hasent got cold yet,hunted the other day -3 with windchillfor about seven hrs,and didnt notice my feet,because they were still warm,just a little info,hope it helps...