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 Merino Wool Base Layer Men's Bottom Pants are made from 100% Merino wool, which is known for being super soft and comfortable. This model is available in different weights—lightweight, midweight, and heavyweight—offering options for various weather conditions. The midweight option (250 g/m²) strikes a good balance for most uses. The material is highly effective at moisture-wicking and odor resistance, keeping you dry and fresh throughout the day.

The wool's natural properties also help regulate body temperature, making these pants suitable for year-round wear. The fit is designed to be comfortable with a pull-on closure, and the superfine 17.5-micron wool ensures that there's no itchiness, which can be a common issue with some wool products. The pants are durable and can be machine washed, although hand washing and air drying are recommended for longer life.

One of the perks is that they come with Merino wool hiking socks, adding extra value. Potential downsides include the need for specific care instructions to maintain durability, and as they are imported, this might affect some buyers' preference for locally made products. These pants would be a great choice for anyone needing reliable and comfortable long underwear, especially for outdoor activities. They also make for a thoughtful gift due to the cool packaging.