10 Best Warmest Mens Long Underwear 2025 in the United States

The Thermajohn Long Johns Thermal Underwear set is an excellent choice for men seeking warmth and comfort during cold weather. One of its standout features is the ultra-soft fleece lining, which effectively locks in heat, making it ideal for chilly days. The breathable fabric also excels in moisture-wicking, ensuring you stay dry by pulling sweat away from the skin, which is great if you're active or layering up.

The fit is designed with 4-way stretch material, allowing for a full range of motion without discomfort from chafing or bunching, making it suitable for both outdoor activities and lounging at home. Additionally, its construction seems durable, which is essential for long-term use, especially during harsh winter months.

While the fabric composition of 92% polyester and 8% spandex enhances comfort and stretch, some users may find polyester less breathable than natural fibers, especially for prolonged use. There's also a chance that the fleece lining can feel bulky under tight-fitting outer layers, which might not suit everyone's preference when it comes to fitting. In terms of care, it's machine washable, which adds to its convenience. However, being imported from China might raise concerns about sustainability for some consumers.

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 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.