I picked up these mittens for use in cold-weather biking in Boulder as well as to keep me warm while hiking in the Rockies from about 20F and lower temperatures. I've used them a on several hikes and a bunch of days biking and they work really well! They're pretty weatherproof and they're extremely warm. There's plenty of room to put liner gloves or mittens underneath them. The cuffs are nice and fit over most jackets (probably not a huge parka though) and the tightening system works really well to keep cold air out.Some specifics: I've used them at about 12,000 feet in temperatures that were probably about 10F with a pretty strong wind and my hands were still quite warm. I'm going to continue using them throughout the winter and think they'll perform quite well.