10 Best Thermals For Winter 2026 in the United States

The Merino.tech Merino Wool Base Layer Women Set is designed to keep you warm and comfortable during cold weather, making it a solid choice for winter thermals. Made from 100% superfine merino wool, this set feels soft against the skin and avoids the itchiness often associated with wool. It comes in a midweight option (250 gsm), which strikes a good balance between warmth and breathability, suitable for moderate to cold winter conditions. The fit is regular and true to size, with a crew neck and long sleeves that make it easy to layer under outerwear without bulk.

One of the biggest benefits of merino wool is its natural moisture-wicking and odor-resistant properties, and this set does a great job keeping you dry and fresh even during active use like hiking or outdoor work. It’s also lightweight enough to layer comfortably with other pieces for added warmth. On the care side, the fabric is durable but requires gentle handling—hand washing and flat drying are recommended to maintain its quality over time. While the set has low stretch, it still offers good mobility for most daily activities. The included merino wool hiking socks add extra value, especially for those spending long hours outdoors.

Some might find the midweight option less insulated than heavyweight alternatives if they face extremely cold conditions, but for most winter activities, it provides reliable warmth without overheating. This base layer set is well suited for women looking for comfortable, breathable, and natural thermal underwear that performs well in varied cold weather scenarios.

The Merino.tech Merino Wool Base Layer Set for men is a strong choice for anyone needing reliable warmth in cold weather. Made from 100% superfine merino wool, this set offers a soft, comfortable fit without the itchiness often found in wool products. It comes in three weights (lightweight, midweight, heavyweight), with this particular midweight version striking a good balance for cold but not extreme conditions. The fabric naturally wicks moisture away and resists odors, helping you stay dry and fresh during physical activity or daily wear.

Its breathable nature also means it helps regulate body temperature, reducing the risk of overheating. The set includes a top, bottoms, and even merino wool hiking socks, adding extra value and enhancing layering options. While it’s machine washable, hand washing and air drying are recommended to maintain durability over time. This base layer fits well as an all-around winter thermal, ideal for hiking, skiing, or everyday outdoor use in cold climates.

One possible drawback is the need for gentle care to keep the wool in good shape, which might be a bit more effort than synthetic alternatives. But for those prioritizing natural fibers, comfort, and moisture control, this set delivers excellent performance.

The Merino.tech Merino Wool Base Layer Set for men is made from 100% superfine merino wool, known for its softness and comfort, which minimizes itchiness common with other wool products. Available in three weights—lightweight (165 g/m²), midweight, and heavyweight—this particular set is the lightweight 165 gsm, ideal for moderate cold or as a versatile layering piece under other winter clothes. The fit is regular and true to size, offering good coverage with long sleeves and long johns, making it suitable for most body types without being tight or restrictive.

Its natural moisture-wicking properties help keep you dry by pulling sweat away from the skin, while the wool's odor-resistant nature means you can wear it for extended periods without it smelling. This makes it practical for activities like hiking or long days outdoors. The fabric doesn't have stretch, so while the fit is comfortable, it may not offer as much flexibility as synthetic blends.

In terms of layering, its lightweight design works well under heavier garments without adding bulk, though those needing more insulation in very cold climates might prefer the midweight or heavyweight versions. Durability is decent for merino wool, but gentle care like hand washing and flat drying is recommended to maintain its softness and shape over time. Also, the set includes a free pair of merino wool hiking socks, adding value. This base layer suits men looking for a natural, comfortable thermal for winter use that balances breathability, moisture control, and softness. For those needing more stretch or heavier insulation, other options or thicker weights in this brand's line may be preferable.