10 Best Thermal Underwear 2025 in the United States

The Merino.tech Merino Wool Base Layer set for men is made from 100% superfine merino wool, known for being soft and comfortable without causing itchiness. This set comes in three weights—lightweight, midweight, and heavyweight—with the described option being the heavyweight at 320 g/m², making it well-suited for very cold conditions. The fit is designed for daily wear, avoiding bunching or overheating, which helps keep you comfortable under other clothes.

One of the strongest points of this product is its natural moisture-wicking and odor-resistant properties, keeping you dry and fresh even during active use. The fabric breathes well, helping regulate body temperature across different seasons. It includes a pair of Merino wool hiking socks, adding value to the package. Durability-wise, while merino wool is naturally resilient, the recommendation to hand wash and lay flat to dry means it may require more care than synthetic options. Machine washing is mentioned but hand washing is preferred to maintain quality longer.

This set provides a high-quality, all-natural thermal underwear option that balances warmth, comfort, and odor control, especially suitable for outdoor activities or chilly weather. However, those seeking very low-maintenance or budget options might find it less convenient due to care needs and premium material costs.

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 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.