Ultrawarmth diving boots feature Ultrawarmth Celliant® Infrared Thermal technology embedded in the inner material. Celliant® is scientifically proven and approved by the FDA to save body heat and accelerate thermal recovery. The high performance sole offers increased durability and stability. The feet have a hard-wearing toe and heel cap. With the rugged zipper and wide gussets and ELASTEK full stretch neoprene around the ankles and calves, they adapt to all lower leg shapes and sizes.