10 Best Thermal Underwear Sets 2026 in the United States

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.

The Fruit of the Loom Men's Recycled Premium Waffle Thermal Underwear Bottoms offer a comfortable and practical option for staying warm in cold to moderately cold weather. Made from a soft waffle-knit fabric combining 52% cotton and 48% recycled polyester, they provide good insulation without feeling bulky. The material mix helps wick away moisture and dry quickly, which is great if you tend to sweat or wear them for active use. The fit is pull-on style, which makes them easy to wear under other clothing, though they may not be as snug as some performance-focused thermals. Reinforced flat seams contribute to durability and reduce irritation from chafing. While the fabric doesn’t specifically mention odor resistance, the polyester content and quick-dry properties can help keep odors in check during moderate use.

These long johns are ideal for everyday winter wear or layering during outdoor activities but might not be the best choice for intense cold or high-performance sports. The value is enhanced by available multi-packs, making them a practical investment for those seeking warmth and comfort without a premium price.

The Merino.tech Merino Wool Base Layer Men’s Set is made from 100% superfine 17.5 micron merino wool, a top-quality material known for being soft and comfortable without causing itchiness. This set comes in different weights, with the midweight version at 250 g/m² offering a good balance of warmth without overheating, making it suitable for cooler conditions or active outdoor use. It includes both a top and long john bottoms, plus a bonus pair of merino wool hiking socks, which adds value.

The natural moisture-wicking ability of merino wool helps keep you dry by pulling sweat away from your skin, and its odor-resistant properties allow for extended wear without developing smells. The fit is designed for comfort with no rubbing or bunching, important for base layers worn close to the skin. Additionally, the fabric breathes well, aiding in body temperature regulation so it can be worn across different seasons.

This set requires gentle care—hand washing and air drying are recommended to maintain durability and shape, which might be less convenient than machine washing. Imported and offered with a gift-quality presentation, the Merino.tech set provides quality and performance, making it a solid choice for men needing reliable thermal underwear for hiking, winter sports, or everyday cold weather comfort.