I used this mitt to climb Cotopaxi in Ecuador. At 19,348ft, it was very cold on the way up and at the top. I tried gloves to keep my hands warm and ended up resorting to these mitts. They were excellent, and I had no problem keeping my fingers warm. The liners on these are nice and toasty and coupled with glove liners and the idiot straps on the mittens, I felt that I could do whatever rope work I needed to do without exposing my hands to the cold. My only complaint, and the reason I give them a 3 instead of a 5, is that I noticed a slight tear on the inner liner. I was really disappointed in this, because I take excellent care of my gear. Nothing a bit of duct tape couldn't fix, but I have no idea how this happened, because I never removed the liners while on the trail. But in terms of warmth, I would go with them again. One of my teammates used Black Diamond Guide Gloves and she was very happy with them. So, I'm hoping it was a one-of thing.