10 Best Warmest Mens Long Underwear 2025 in the United States

The Merino.tech Merino Wool Base Layer Men's Set is designed to offer comfort and warmth with its 100% superfine merino wool construction. Available in various weights, this midweight option at 250 g/m² provides a good balance of warmth without being too bulky, making it suitable for a range of activities. The set includes a top and bottom, plus bonus merino wool hiking socks, adding extra value to the purchase.

The material is soft and designed to be non-itchy, ensuring a comfortable fit for all-day wear without the common issues of bunching or overheating found with regular cotton alternatives. The natural moisture-wicking and odor-resistant properties of merino wool help keep you dry and fresh throughout the day. However, while the breathability and temperature regulation are excellent, the recommended care (hand wash and lay flat to dry) may be inconvenient for some users who prefer machine washing for ease.

Additionally, while durable, care must be taken to maintain the longevity of the fabric. This set is ideal for men looking for a reliable, comfortable base layer for outdoor activities or everyday wear, particularly in cooler weather.

The WEERTI Thermal Underwear for Men is designed to keep you warm in cold weather with a focus on proper layering. Made from 92% polyester and 8% spandex, the material is lightweight yet offers good insulation by trapping body heat. This blend also ensures a snug fit, almost like a second skin, making it comfortable for all-day wear.

The moisture-wicking capability is strong, which helps keep you dry and comfortable by quickly drawing sweat away from the body. This can be particularly useful during active outdoor activities or even when worn as pajama on chilly nights. Durability is addressed with robust seams and 4-way stretch, allowing flexibility without the risk of tearing, so you can move freely without compromising on warmth or comfort.

Its design is versatile enough to be worn under both formal and casual attire, making it a well-rounded option for men looking to stay warm in cold weather. It is especially suited for those who value comfort and flexibility.

The Amazon Essentials Thermal Long Johns Underwear Set offers a slim fit that contours well to the body, making it a good choice for those who prefer close-fitting base layers. Made from a cotton-polyester blend, it balances softness and breathability with lightweight warmth—ideal for layering without feeling bulky. The waffle knit fabric allows for decent airflow, which helps with moisture control but may not match the moisture-wicking efficiency of high-tech synthetic materials.

While cotton can absorb sweat, the polyester content helps reduce that effect somewhat, though this set may not be the best for heavy sweating or intense outdoor activities. The underwear includes elastic waistbands and ribbed cuffs to keep the bottoms snug, which adds to comfort and heat retention. Durability appears reliable for regular daily use, given the trusted Amazon Essentials brand and machine-washable fabric, though it might not hold up as well under very rough conditions or frequent heavy washing.

This set serves as a solid, affordable option for everyday cold weather wear, especially if you want a slim, comfortable fit and moderate warmth, but it might not meet the needs of those requiring advanced moisture management or odor control for strenuous activities.