Connor Merritt

As temperatures plummet and we move into the cold seasons, staying warm and comfortable is a top priority for many. One essential garment that can make all the difference in keeping the chill at bay is thermal underwear. I’ve camped many times in below-freezing temperatures (including one of my favorite-ever trips to Fort Walker as a Boy Scout) and I can personally attest to the importance of thermal underwear in maintaining heat while out in the elements. I can always tell who’s wearing thermal underwear on every cold-weather trip I take: the ones who are shivering and miserable aren’t wearing them, while the people merrily having a blast are the ones who came prepared.

In this article, we explore the importance of thermal underwear and highlight the best options for both men and women.

Common Layering Mistakes

Before I get into thermal underwear, it’s important to understand the basics of staying warm outdoors. Layering is the fundamental idea of how to dress in multiple layers of clothing to keep warm. However, each layer serves a unique purpose — you shouldn’t put five jackets on top of each other after all. The top layer is the shell; this one keeps the elements out and prevents cold from invading personal space. The middle layer insulates your body, keeping the warmth in with softer materials. The final layer, the base, helps to keep you dry by collecting the moisture your body generates and dispersing it through the fabric to keep you warm.

One big mistake that amateurs make when first recreating in the cold, is to wear clothes that keep them too warm, without any consideration for a moisture wicking layer. It might seem odd to say that, but let me explain: Exercising out in the cold while wearing super warm clothes will heat you up and this makes your body sweat in an effort to cool you down. The problem is that this sweat, which would normally evaporate or get wicked off in the summer time, is now trapped inside all those thick layers. Then, once you’re done moving your body and just want to relax, you’re going to be extremely cold and wet due to all that accumulated sweat.

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I can’t tell you how many times I’ve seen someone unused to cold weather outdoors who comes on a trip decked out in nothing but thick cotton shirts, cotton socks, and cotton sweaters, all packed underneath heavy overcoats. Needless to say, they were not having a good time.

Why Thermal Underwear is Important

This is where thermal underwear comes in. Also known as long johns or base layers, it is a specialized type of clothing that provides an additional layer of insulation beneath your regular clothing. These garments are typically made from materials that offer excellent heat retention properties while effectively wicking away moisture, ensuring that you stay dry and warm in cold conditions.

1. Temperature Regulation: Thermal underwear helps regulate your body temperature by trapping warm air close to your skin. This insulation is especially crucial during frigid winter days or when engaging in outdoor activities in cold environments.
2. Moisture Management: High-quality thermal underwear wicks sweat and moisture away from your body, keeping you dry. This moisture-wicking property is essential for preventing discomfort and potential hypothermia in cold conditions.
3. Layering: Thermal underwear serves as the foundation for layering. By adding layers, you create an efficient and customizable system for adapting to changing weather conditions.

Now, let’s explore the top three thermal underwear options for both men and women:

Top Three Thermal Underwear for Men

1. Smartwool Merino 150: Smartwool is famous for its high-quality merino wool products, and the Merino 150 exemplifies this. Merino wool has excellent temperature-regulating properties and moisture-wicking capabilities. The Smartwool Merino 150 offers a snug fit, making it an ideal base layer for cold weather activities. Available starting at $61.22.
2. SITKA Core Lightweight Bottoms and Top: SITKA is a brand synonymous with outdoor enthusiasts and hunters, and their Core Lightweight thermal bottoms and tops can withstand rigorous outdoor conditions. Made from a blend of polyester and spandex, these garments offer a balance of warmth and mobility, making them perfect for active pursuits. Available starting at $59.18.
3. TSLA Men’s Thermal Underwear: TSLA offers budget-friendly thermal underwear without compromising on quality. Their thermal sets are made from a blend of microfiber and spandex, providing warmth, comfort, and moisture-wicking capabilities. With various styles and colors to choose from, TSLA’s thermal underwear is a versatile choice for everyday wear. Available starting at $33.98.

Top Three Thermal Underwear for Women

1. Montbell Super Merino Wool Lightweight: Montbell’s Super Merino Wool Lightweight thermal underwear is made from super-soft merino wool, ensuring exceptional warmth and comfort. The slim fit allows for easy layering under clothing, making them perfect for winter sports or everyday wear. Available starting at $79.00.
2. Uniqlo Heattech Ultra Warm: Uniqlo’s Heattech Ultra Warm collection is famous for its affordability and effectiveness. These thermal pieces use Uniqlo’s innovative Heattech technology, which retains heat and wicks away moisture. The Ultra Warm line is perfect for those seeking warmth without bulkiness. Available starting at $29.90.
3. Smartwool Intraknit: Smartwool’s Intraknit thermal underwear offers a combination of merino wool and synthetic fibers. This blend provides excellent insulation and moisture management. The Intraknit technology ensures a perfect fit and comfort, making it an excellent choice for outdoor activities. Available starting at $130.00.

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