Originally produced to meet U.S. Army specifications, this one-piece, full-body men's long underwear is popular with construction site workers, hunters, fishermen and others who spend extended periods of time outdoors in cold weather. The heavyweight fleece lining traps body heat, while the smooth face makes it easy to slide extra layers on or off. Thermoregulation technology keeps you warm in a wide range of conditions, and ClimaSense fabric fusion helps you maintain an optimal body temperature as your activity level changes throughout the day.