10 Best Thermal Underwear 2025 in the United States

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.

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 WEERTI Thermal Underwear for Men is designed to keep you warm and comfortable during cold weather, making it a solid choice for anyone needing reliable base layers. Made from a blend of 92% polyester and 8% spandex with a fleece lining, this set offers good insulation by trapping body heat while staying lightweight. The snug fit is like a second skin, which helps minimize heat loss and works well under various types of clothing, from casual wear to more formal outfits.

One of its strong points is the moisture-wicking fabric that effectively pulls sweat away from the skin, keeping you dry and preventing that uncomfortable clammy feeling. The material also stretches in all directions, allowing freedom of movement without feeling restrictive, and the seams are designed to be durable, lowering the risk of tears during active use.

This thermal underwear performs well for men seeking a comfortable, warm, and moisture-managing base layer suitable for winter activities or simply staying cozy indoors.