8 mm neoprene provides comfort and flexibility, along with excellent waterproofing, shock absorption and heat retention properties; adjusts to your foot shape to resist blisters and chafing Muck's warmest boot; fleece lining is soft, durable and provides exceptional warmth in extreme cold; 2 mm thermal foam under the footbed for extra warmth; comfort rated from -60 °F to 30 °F (-50 °C to -1 °C) Stretch-fit Comfort Topline snugs calf to seal in warmth while keeping cold and debris out; double reinforcement in the instep, heel and Achilles area where you need it most Lightweight EVA midsole for additional cushioning; super aggressive Bob-Tracker outsole is rugged and durable High-grade rubber provides extra toughness and makes for a 100% waterproof hunting boot; Shaft Circumference is 17 inches; rear pull loops for easy on/off