10 Best Thermal Underwears 2025 in the United States

The Merino.tech Merino Wool Base Layer Men's Set is a solid choice for anyone needing reliable thermal underwear, especially for outdoor activities or cold weather. Made from 100% superfine merino wool, it offers excellent softness and comfort without the itchiness common to wool. This set comes in three weights—lightweight, midweight, and heavyweight—letting you pick the right warmth level for your needs; the midweight 250 g/m² option included here is versatile for most cool conditions.

The natural moisture-wicking ability of merino wool helps keep you dry by absorbing sweat better than many other fabrics, and it also resists odors, which means you can wear it longer without worrying about smell. The fit is designed to avoid bunching or overheating, making it good for active wear throughout the day. Plus, the package even includes a pair of merino wool hiking socks, adding value.

On the downside, merino wool requires gentle care—hand washing and air drying are best to maintain softness and longevity, which might feel like extra work compared to machine-wash-only fabrics. Some users might find the price a bit higher than synthetic options, but the natural benefits typically justify it. For those seeking a comfortable, breathable base layer that keeps you warm and fresh, this merino wool set is a dependable pick.

The Cuddl Duds AMAZON WMS TP - L/S Black thermal underwear set is designed for cold weather, featuring a brushed fleece inside and a soft matte outside for added comfort. Made from a blend of 93% polyester and 7% spandex, it offers good stretch and flexibility, ensuring a snug fit that can move with you.

The spandex stretch and modern rise leggings provide on-the-go comfort, while the thumbhole sleeve top and tag-free label enhance wearability throughout the day. The set also includes moisture-wicking fabric, which helps absorb and evaporate moisture, keeping you dry and comfortable. Additionally, it offers 50+ UV protection, adding an extra layer of defense against harmful rays.

Weighing in at 14.89 ounces, it is lightweight enough to wear as a base layer or on its own. However, the heavyweight fabric might feel too warm in milder temperatures, and while it is machine washable, the 93% polyester composition may not be as breathable as natural fibers. Ideal for those who need reliable and warm thermal underwear for outdoor activities or everyday use in colder climates.

The WEERTI Thermal Underwear for Men offers a lightweight but warm base layer, made from a blend of 92% polyester and 8% spandex. This combination provides a snug, stretchy fit that acts like a second skin, helping to trap body heat efficiently while allowing flexibility for movement. Its fleece lining adds extra warmth without making the underwear bulky, which is great for layering under different outfits or wearing as cozy pajamas.

One of the standout features is its strong moisture-wicking capability, which helps keep you dry by quickly pulling sweat away from your skin—this is especially useful for active use or long wear in cold conditions. The seams are designed to be durable, reducing the chance of tears through daily activities. While the fabric is synthetic, it’s breathable enough to avoid that clammy feeling common with some thermal underwear. However, those who prefer natural fibers like wool might find this less comfortable or less odor-resistant over time.

This set suits men looking for an affordable, reliable thermal base layer that balances warmth, moisture control, and freedom of movement during winter or chilly weather. The fit is quite form-fitting, so sizing up may be necessary for those who want a looser feel or plan to wear it over other layers.