10 Best Thermal Underwear 2026 in the United States

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.

The Merino.tech Merino Wool Base Layer Mens Set is a solid choice if you want reliable and comfortable thermal underwear made from 100% superfine merino wool. It comes in a midweight option (250 g/m²), which strikes a good balance for staying warm without feeling bulky—ideal for cooler weather or active outdoor use. The wool is soft and itch-free, making it comfortable for all-day wear, which is a big plus since some wool products can feel scratchy. Thanks to natural moisture-wicking, it helps keep you dry by pulling sweat away from your skin, and its odor-resistant qualities mean you can wear it longer without smelling, which is especially handy for hiking or multi-day activities.

The fit is designed to avoid bunching or overheating, adding to comfort during movement. It also comes with a free pair of merino wool hiking socks, which adds good value. One downside is the care instructions: while the label says machine wash, hand washing and laying flat to dry are recommended to maintain durability and shape over time, which might be a bit more effort than some users prefer.

While midweight is versatile, if you need extreme cold protection or very light layering, you would need to look at their heavyweight or lightweight versions separately. This set suits men looking for breathable, comfortable thermal underwear with natural performance features, especially for outdoor activities or extended wear.

The WEERTI Thermal Underwear for Women is designed as a base layer to keep you warm and dry in cold weather. Made from 92% soft polyester and 8% spandex with a fleece lining, it offers a cozy feel and good insulation while remaining lightweight. The fleece lining adds warmth without bulk, which is great if you want to layer under your jackets or sweaters. Its four-way stretch fabric provides flexibility, hugging your body nicely to allow easy movement without feeling tight or restrictive.

A strong point of this thermal underwear is its moisture-wicking ability, which helps pull sweat away from your skin to keep you dry and comfortable during activities. The snug fit also helps reduce heat loss and prevents bunching, making it practical for wearing under both casual and formal clothes, or even as pajamas. The design focuses on comfort and minimizing skin irritation, which is important for all-day wear.

The fabric blend is soft and stretchy, though it might not offer the highest durability compared to some thicker or technical fabrics, so it may show wear over time with frequent use. This thermal underwear is a good choice if you want a lightweight, flexible, and warm base layer that fits well and manages moisture effectively. It suits women looking for comfort and warmth in cold weather, especially for layering under everyday clothing, though it may not be the best option if you need heavy-duty durability or advanced odor control.