I noticed a few people mentioned Muck Arctic boots (Arkansas Paul and Armored Farmer) as being very warm. I looked at a pair for my daughter and it doesn't appear there is any insulation (no Thinsulate or similar). Is the neoprene really that good of an insulator?
I'm sold on Muck boots! They are very warm, and surprisingly comfortable to walk in. Plus calf high is great in deep snow and when crossing streams. Compare weights with knock-offs, the Mucks are significantly lighter from what I've seen.
The warmest boots are the felt packs, like Sorels. But they are heavy and bulky which makes walking a chore. And when its bitter cold a nice hike every so often warms the other body parts up.