10 Best Thermal Underwear 2025 in the United States

The Cuddl Duds Thermal Underwear set for women is designed to keep you warm and comfortable during cold weather. Made from a soft, heavyweight blend of polyester and spandex, it provides a cozy fleece lining inside with a smooth, stretchy exterior that moves with you. The spandex stretch ensures a snug but flexible fit, making it easy to wear under clothes or on its own.

It features moisture-wicking fabric that helps pull sweat away from your skin to keep you dry, which is great for active days. The thermal set also offers protection from UV rays, which is a nice bonus if you’re outside for long periods. The comfortable design includes thoughtful touches like thumbholes and a tag-free label to reduce irritation.

While the material blend supports some odor resistance and durability, it's mainly polyester-based, so it may not be as long-lasting as natural fibers like wool. The set is lightweight enough to avoid bulk while still providing good insulation. This thermal underwear is best suited for women looking for a versatile, warm base layer that balances comfort, stretch, and moisture management for everyday cold weather use.

The Cuddl Duds Thermal Underwear set for women is designed to keep you warm in cold weather with a cozy brushed fleece lining and a soft matte exterior. Made from a blend of 93% polyester and 7% spandex, it offers a nice balance of warmth and stretch, making the fit comfortable and flexible for everyday activities. This two-piece set features moisture-wicking fabric that helps keep sweat away, which is great if you tend to get warm during physical activities or layering. The fabric is also tightly knit, providing protection from UV rays, a nice bonus if you spend time outdoors.

The thumbhole sleeves and modern rise leggings add to the practical and comfortable fit without adding bulk, allowing you to wear the set both as a base layer or on its own when lounging. At just under 15 ounces, it's lightweight enough for layering without feeling heavy. This thermal set is a suitable choice if you want a soft, stretchy, and warm outfit that works well for casual cold-weather wear, though for intense winter sports or heavy-duty use, you might want to look for additional durability features.

The Merino.tech Merino Wool Base Layer Mens Set stands out with its use of 100% superfine merino wool, known for being soft and itch-free, ensuring all-day comfort. This set includes both a top and bottom in midweight (250 g/m²), making it versatile for varying temperatures. Additionally, the package includes a bonus pair of merino wool hiking socks, adding extra value.

The natural moisture-wicking and odor-resistant properties of merino wool make this thermal underwear an excellent choice for staying dry and fresh during active use. Its breathability helps regulate body temperature, providing comfort throughout the year. Despite being machine washable, hand washing and air drying is recommended for extended longevity, which might be inconvenient for some users.

The fit is designed to prevent rubbing, overheating, or bunching, contributing to comfort. This set would be particularly beneficial for men needing reliable and comfortable base layers for outdoor activities or everyday wear in cooler climates.