Not sure how you can rate a boot for 70 to -20 unless it had a built in air conditioner. Hands down for warmth and dryness you can't beat Mickey Mouse boots only bad thing is they are heavy to lug around if walking alot, but for sitting a stand you won't find anything wamer, if your doing alot of walking the insulated zipper Northerners can't be beat I have been thru about 6 piar in my life time and find them to be the BEST all around hunting boot there is, they are light and water proof, easy on and off and they are warm, not as warm as a Mickey but warm enough for moving about, I have ice fished in mine and can stay warm standing on the ice for about 3 hours then need to move around alittle.........her is where I get them from http://www.hanksclothing....nsulated_zip_pac_buy.html imageI don't think you would be disappointed at all with them..................