10 Best Thermal Underwear Sets 2025 in the United States

The Thermajohn Long Johns Thermal Underwear Set for Men, available in Medium and Navy, is designed to keep you warm and comfortable in cold weather. Made from a blend of 92% Polyester and 8% Spandex, the material is lightweight yet effective in retaining heat. The ultra-soft fleece lining adds an extra layer of comfort, making it suitable for everyday wear or even as pajamas.

The set is breathable and features moisture-wicking properties, which help keep you dry by wicking away sweat and moisture. This is a great feature for active users or those who may wear it for extended periods outdoors. The 4-way stretch material ensures a good fit, allowing freedom of movement without chafing or bunching up. This makes the underwear set versatile for various activities, from lounging to engaging in outdoor sports.

The set is machine washable, making it easy to care for. This thermal underwear set is ideal for anyone needing an extra layer of warmth, especially those who value comfort and flexibility in their clothing.

The Merino.tech Merino Wool Base Layer Women Set offers a versatile option for those looking for thermal underwear. Made from 100% Merino wool, the set is available in three different weights—lightweight, midweight, and heavyweight—making it adaptable for various temperature conditions. The midweight version, at 250 g/m², strikes a good balance between warmth and breathability, suitable for moderate cold weather activities. The included hiking socks add extra value to the package, making it a thoughtful gift option as well.

One of the standout features is its moisture-wicking and odor-resistant properties, which help keep you dry and fresh throughout the day. The natural breathability of Merino wool also aids in temperature regulation, ensuring comfort across different climates. However, the set requires careful maintenance, including hand washing and air drying, which might be inconvenient for some. Another point to consider is the product's origin from China, which may be a factor for those who prefer locally made goods.

On the fit side, the superfine 17.5-micron wool ensures a soft and comfortable feel without itching or bunching, which is a plus for daily wear. While the durability is generally good, following the care instructions diligently is essential to maintain its quality. This Merino wool base layer set is excellent for those who prioritize comfort, moisture management, and odor resistance, though the care requirements and origin might be minor drawbacks for some.