Functional underpants together with the functional undershirts form the clothing layer of functional underwear. The thermal underpants can be used as the first layer of clothing for outdoor and winter sports such as skiing, snowboarding, hiking or mountaineering. These underpants have a high absorbency, thermoregulating and sweat transporting effect. Thus, the body remains dry during sports and cools down less quickly or does not warm up too quickly. Functional underpants from manufacturers such as Odlo, X-Bionic, Craft or Icebreaker are made of synthetic or natural fibers such as merino wool.