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 choice for women looking for comfortable and effective long underwear to stay warm in cold weather. Made from 100% superfine merino wool, this midweight set feels soft on the skin and avoids the itchiness some wool products can cause. The fabric's natural moisture-wicking ability helps keep you dry by pulling sweat away, while its odor resistance means it stays fresh even after extended wear.

This set fits true to size with a modern, regular fit that doesn’t bunch or rub, making it comfortable for daily use or outdoor activities like hiking. It’s breathable and regulates your body temperature well, so it works in various conditions, not just deep winter. The added merino wool hiking socks in the package are a nice bonus for active users.

On the maintenance side, hand washing and air drying are recommended to keep the garment in good shape longer, which might be a bit less convenient than regular machine washing. The midweight fabric strikes a good balance, but those needing extra warmth might want to consider the heavyweight option. This base layer is durable, comfortable, and practical for anyone who spends time outdoors or needs reliable cold-weather underwear.