10 Best Long Underwear For Cold Weather 2026 in the United States

The Merino.tech Merino Wool Base Layer Set is a solid choice for anyone needing warm, comfortable long underwear for cold weather. Made entirely of superfine merino wool, it offers excellent softness and comfort without the itchiness commonly found in wool garments. The heavyweight option, at 320 gsm, provides strong insulation, making it ideal for very cold conditions. Thanks to natural moisture-wicking and odor-resistant properties, this set keeps you dry and fresh during extended wear, which is great for active outdoor use or layering under winter clothing.

The fit is true to size and regular, so it should suit most body types without feeling too tight or loose. One minor downside is the low fabric stretch, which may limit flexibility during highly dynamic activities. Care instructions recommend hand washing and air drying to maintain durability and performance, which requires a bit more effort than typical machine washing. The inclusion of merino wool hiking socks adds nice extra value to the package.

For those seeking a reliable, breathable base layer that naturally regulates body temperature and resists odors, this set meets those needs well, especially for colder climates or winter sports.

The Under Armour Men's Performance Tech Long-Leg Boxerjock is designed with a lightweight and soft polyester blend that helps keep you comfortable as a base layer in cold weather. Its slim fit is true to size, providing a snug but not too tight feel that allows easy movement thanks to the 4-way stretch fabric. The material is breathable and quick-drying, which helps wick away moisture to keep you dry during active use, an important feature for cold weather layering.

It also has chafe-free seams and a no-roll hem, improving comfort during long wear. Since it’s lightweight, this long underwear may not provide heavy insulation on its own, so it’s best paired with additional layers in very cold conditions. This product suits those looking for comfortable, moisture-wicking base underwear that moves well and feels soft against the skin, ideal for moderate cold or active outdoor activities.

The Merino.tech Merino Wool Base Layer Set is a solid option for anyone looking for comfortable and effective thermal underwear for cold weather. Made from 100% superfine merino wool, it offers a soft feel that won’t irritate the skin, which is a significant strength for daily wear. With a midweight of 250 g/m², it strikes a good balance between warmth and breathability, making it suitable for various outdoor activities, from hiking to simply lounging around in chilly conditions.

One of the standout features of this base layer is its moisture-wicking capability. Merino wool excels in managing moisture, allowing it to keep you dry and fresh even during physical activities. Additionally, its natural odor-resistant properties mean you can wear it for longer periods without worrying about unpleasant smells, which is ideal for active users.

There are a few drawbacks to consider. While the set is durable, proper care is essential; it requires hand washing and laying flat to dry to maintain its longevity. This might be inconvenient for some users who prefer machine wash-friendly options. Also, while the midweight fabric is versatile, individuals seeking ultra-heavyweight options for extremely cold conditions might find it less suitable. The added bonus of receiving Merino wool hiking socks with the set is a thoughtful touch, enhancing its value as a gift or personal purchase. This Merino wool thermal underwear set can meet the needs of outdoor enthusiasts or anyone needing extra warmth in cold weather with its blend of comfort, functionality, and quality.