Thermal underpants are commonly made from polyester-based and cotton/recycled-polyester blends. Typical formulations shown in listings include 95% polyester/5% spandex, 90% polyester/10% spandex, 88% recycled polyester/12% spandex, and 60% cotton/40% recycled polyester, as well as plain polyester and polyester–spandex constructions.
Many thermal underpants use fleece-lined or other soft insulating inner layers. Listings frequently describe a fleece lining or soft insulating fleece specifically designed to trap and retain body heat.
Thermal underpants commonly come in lightweight and midweight constructions: lightweight thermals for layering and midweight knit fabrics for added warmth.
Thermal sets commonly include two matching pieces: a long-sleeve top and bottoms. Individual pieces are also available, but two-piece shirt-and-pant sets appear frequently in listings.
Several listings highlight moisture-wicking fibers and soft-touch polyester blends to help manage sweat while retaining warmth. Other common performance notes include stretch for active movement and durable stitching for long-term wear.
Listings recommend thermal underpants for cold-weather and winter activities such as skiing, snowboarding, sledding and other slope activities, as well as general cold-weather wear and indoor lounging.
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