How to Choose a Base Layer

The basics of base layers – what they do and how to choose the right one for you.

The base layer, a fundamental piece of your winter wardrobe... and the rest of the year as well
One of the basic components of the layering system for outdoor clothing, the base layer is in direct contact with your skin and its main function is to manage sweat and moisture. One of the challenges of mountain activities is that your body warms up as it moves, often leading to heavy sweating. Sweat evaporates, absorbing heat from your body to keep you cool. This natural cooling system works well in mild or high temperatures. However, in extreme cold or during long-term activities where you alternate between intense aerobic activity and rest, this cooling can be a problem. Your body can absorb too much heat when your clothes soak up sweat, causing a drastic drop in body temperature. It can even be dangerous and result in hypothermia.

This is where a base layer comes in. Its role is to move sweat away from the body, where it can harmlessly evaporate away, keeping the body dry and warm. Which is why you need a good base layer, and not just any material will do.

When it comes to choosing your base layer, you have several materials to choose from, each with its advantages and disadvantages. Depending on the intensity and duration of the activity, some materials are more appropriate than others.


First things first: forget about the cotton for any long activity or in cold conditions. Cotton is the worst material for a base layer. The problem with cotton is that it is a hydrophilic fabric. From the Greek "Hydro" (water) and "Philo" (friend), these fabrics absorb water and dry slowly. Which means a hydrophilic fabric like cotton soaks in sweat, trapping body heat and making it impossible to maintain an adequate temperature, increasing the risk of hypothermia and other serious issues. There's a reason people say "Cotton kills", because in the mountains it does.

For a suitable base layer, you have to choose from the range of hydrophobic fabric options below. Hydrophobic fabrics resist water penetration, and dry quickly with minimal absorption. Thanks to these characteristics, they manage to wick moisture away from the body to keep you as dry (and therefore as warm) as possible.

LIFA fabric from Helly Hansen. Modification of the original from 1970, fully hydrophobic

Introduced in the market in the 1970s, today there is a variety of different synthetic fabrics to choose from, including polyester, nylon, elastane, polyamide and polypropylene. Each one has different features and nuances, but in general they have a good stretch, keep their shape well and provide a snug fit. Synthetic garments are the best at at wicking away moisture and are also the most resistant and durable.

Odlo Suw Top Performance Light LS W
The disadvantages of synthetic fibers are that they absorb more bacteria that produce odors if worn for multi-day trips without washing in-between. They're also not as soft on the skin as natural fabrics and chafe easier against sensitive areas. This combination makes synthetics perfect for intense aerobic activities and shorter trips, when wicking away moisture takes priority over the comfort required for a multi-day adventure.


Merino Wool

Another option for a base layer is merino wool. Following the trend toward natural and sustainable values in many industries, merino wool has been gaining ground against synthetics since it hit the market in the 1990s. Unlike traditional heavy wool that has thick, coarse fibers that irritate the skin, merino wool is lighter and more flexible, around 13-25 microns thick. That makes it three times thinner than a human hair or half as thick as a traditional wool fiber. These fine and delicate fibers are transformed into a final product that is much softer on the skin, with a number of features that make it a great base layer.

The threads of merino wool are almost microscopic.
A natural fiber, merino wool has many advantages over synthetic fibers. It’s highly breathable and warm, perfect for cold conditions. Interestingly enough, its properties make it a good fabric for warm weather as well, and helps cool down the body. Wool is also naturally bacteria- and odor-resistant, so it’s a good choice if you’ll be working up a sweat. Finally, it is a natural material made from a renewable and sustainable source, unlike synthetic fabrics, which are petroleum-based.

Up close detail of merino wool.
On the other hand, although merino wool wicks away sweat proficiently enough, it is slower to dry than synthetic fibers. Moreover, it is less resistant and durable than synthetics (especially considering its higher price tag), and more susceptible to damage from abrasion from rocks and backpacks, for example. Lastly, its natural fibers can also suffer from pests like mites and moths.

All this makes merino wool perfect for less intense, longer activities (multi-day trips where washing may not be an option) and in colder conditions.

Brands like Devold and Odlo from Norway, Patagonia from the United States, and Icebreaker from New Zealand are leading brands in the use of merino wool in their high-quality garments.



Hybrid fabrics feature different blends of merino wool with synthetics. Mixing merino and synthetics in one piece combines the best aspects of both materials and attempts to minimize drawbacks. For example, the touch, warmth and antibacterial properties of merino wool are combined with the quicker drying capacity and increased durability of a synthetic fiber. There are a variety of combinations with different blends of natural and synthetic on the market, each providing a unique set of advantages.

Hybrid fabric, with a merino wool fiber wrapped around a synthetic fiber.
Another factor to consider when shopping for a base layer is size and fit. A base layer, one that moves the most sweat away from the body, must have a snug but not constricting fit that rests against your skin. A quality base layer will have a seamless or flat-seamed design won’t chafe your skin even as it hugs your body.

"Anti-chafing" flatlock
Another factor that you should take into account is the garment's thickness, or fabric weight. Base layers come in different options, normally lightweight, midweight and heavyweight. Choose a thickness based on how cold it is and how active you expect to be. Remember that the main function of a base layer is not to retain heat, but to wick away sweat. So if you're planning on an intense activity in cold conditions, choose a slightly thinner layer than if you are going take more rests in warmer temperatures. On the other hand, lightweight layers are less resistant and durable than a heavyweight ones.

Devold Hiking M Boxer.

Now that you're familiar with the concept of a base layer, what it's for and the different fabrics you can choose, be sure to visit Barrabes online to see the specific models available and choose the best option for your needs. Remember that a base layer is just that – an inner layer. Base layer garments aren't designed to be worn as an outer layer and never directly under a backpack if you want them to last. They are rather delicate, designed to be in contact with your skin. The abrasion that comes from outdoor conditions, rocky terrain or your backpack’s shoulder straps will drastically shorten the life of these garments, so make sure you always wear them correctly.

For more information about base layers, contact Barrabes customer service, or shop our online store:

Men’s Base Layers

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Women’s Base Layers

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