Long underwear, also known as thermal underwear, is a type of clothing designed to provide warmth in cold weather. It is typically made from materials like cotton, wool, or synthetic fibers that trap body heat while allowing moisture to escape. Long underwear usually consists of a top and bottom, fitting snugly against the skin. This clothing is commonly worn as a base layer under regular clothes during winter activities such as skiing, hiking, or simply staying warm at home. Long underwear is available in various styles and thicknesses, catering to different levels of cold exposure and personal comfort preferences.