The Muck Arctic Sport Extreme Conditions Sport Hi Boot has a comfort range of -40°F to 60°F. This boot has all the standard Muck Boot features plus much more. The stretch-fit topline binding snugs the calf to keep warmth in and cold out. The MS-1 molded outsole is rugged, aggressive and durable for maximum protection and stability. It is 100% waterproof, lightweight and flexible.