This boot does a pretty good job of keeping your feet warm under less than severe conditions.  The tag in the box said good up to -32, but I doubt these boots would do a very good job in those conditions.  I got these boots to wear in Soldier Field, sitting with feet on cold concrete for 3 1/2 hrs at a Bears game.  Worked well for that in temps of the mid to upper teens in January.  Got a little cold towards the 4th quarter, but walking around a little warmed them up enough.  Boots are comfortable, but run small, as others have said.  I got a full size larger than my normal shoe so I could fit 2 pair of wool socks, and they're just right.  The insulation may pack out over time, so they could end up being a little big, but for cold weather too big is always better than too small.  They are waterproof enough for shoveling snow and walking the dog.  Don't know how they would be in heavy duty use in deep snow, but seem like they would be good winter hiking boots.