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Layering for Cold Weather: The Base Layer

When the temperature dips, many of us head to our closet for those all important base layers. Whether you refer to them as long johns, thermals or base layers, they all provide the same important function when the weather turns–keeping you warm. Worn as a first layer directly against the skin, base layers should be form fitting but not tight to the point where they constrict blood flow. Like any item worn against the skin, they insulate by holding a layer of warm air close to the body. This air is kept from escaping by clothing layered above.

Base layers are often constructed of cotton, polyester or merino wool. While each of these provide warmth, each has their drawbacks. Cotton, for one, makes for a thermal that is both soft and warm; cotton base layers also tend to be the cheapest on the market. One drawback with cotton, and a significant one at that, is that when wet, cotton fibers adhere to one another, which decreases the airspace between the strands. Without those pockets of air wet cotton base layers can not trap heat, which in turn causes the fabric to cling to the skin, resulting in rapid cooling of the body through conduction.

Like cotton, polyester base layers are relatively inexpensive and tend to be the lightest weight thermals on the market. Polyester is also popular due to its hydrophobic qualities. This characteristic aids the “wicking” of moisture from the skin, enabling the body’s efforts to regulate temperature. While these properties make for great value, the drawback with poly base layers is that they tend to develop odor over time. As part of the manufacturing process, these products are treated with an additive which mitigates the growth of odor causing bacteria. Over time, however, this treatment degrades leaving the wearer with a rather smelly base layer.

Merino base layers are made from the fine undercoat of the merino sheep–a textile that has been used for thousands of years and is both all natural and sustainably harvested. While merino is far and away the most expensive base layer on the market (typically twice the price of a comparable weight synthetic one) merino base layers excel in a couple of key areas, making them a great investment. For one, merino is a highly hydrophobic material that maintains its warmth even when sopping wet. Merino is also a highly durable textile, which means that with a little love, you’ll own it for years. One other characteristic that separates this base layer from others is that it is naturally anti-microbial, meaning that for most people it will never develop odor–ever. Literally, after multiple days of consecutive wear, these base layers remain odor free.

While I prefer merino base layers in most conditions, there are certainly situations where polyester or cotton ones make sense. For example, if you’re on a budget and only plan to wear it a couple of times each season, polyester might be the way to go. Or, if you’re home and just want something soft to lounge in, cotton base layers are great. In a nutshell, you’ve got options when it comes to base layers. Just choose the one that’s right for your wallet and the situation.

Avi David Edelson

Owner, Traverse