I had to wear a mustang suit for 30 days out on an icebreaker doing research in the Bering Sea, and I found them to be ridiculously warm. Layer clothes underneath differently depending on conditions. They won't really keep you from getting hypothermia if you're in the water for an extended period of time though as they're not sealed around your ankles, so the cold water will still rush up your legs. But they're definitely better than most typical icefishing garb at delaying it. I hate them with a passion because they were a pain and we were forced to wear them. And if it is 25 or 30 degrees out, they get really hot. But in colder temperatures, they can definitely keep you toasty.