Military Thermals Polypropylene Thermal Crewneck 100% Polypropylene Polypropylene clothing should be washed in cold or warm water and hang to dry, or VERY LOW dryer heat. 100% MADE WITH PRIDE IN THE USA! Will keep you warm and dry in a wide range of environments. Polypropylene provides unmatched moisture wicking and extremely fast drying. Polypropylene has the lowest body heat or thermal conductivity of any traditional apparel fabric including silk, polyester and wool. Polypropylene is the base layer for the Gen I Extended Cold Weather Clothing System (ECWCS)