Thermofill insulation is the most distinctive property of Thermofill underwear. Thermofill membrane is developed by the most renowned research institutes and polymere manufacturers. The structure of Thermofill insulation is unique. The material does not lose its insulation capacity even after many times of washing. The Thermofill insulation doesn't break up like most cotton-wool insulating materials, and therefore it doesn't get lumpy or flattened with use or after washing. The material also keeps most of its insulation capacity even when completely wet. The suit has vent holes in the armpits and on the left arm to assure free circulation of air inside and outside of the underwear, and to allow air control of the dry suit at any ascent speed. The suit has a zipper with double locks, a chest pocket with zipper, as well as large thigh pockets. Elastic fabric in the collar, sleeves and ankles, and a wide waist band. Thumb loops and leg retainers ease dressing.