Ursuit Thermofill Light inderdragt LadyThermofill 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