How to Choose a Base Layer


March 03, 2022


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merino base layer

Every outdoor expert will tell you that the secret to staying warm and dry during an activity is to wear a good base layer. But, what exactly is a base layer? And, how do you choose the right one? Fanny Bellerive, SAIL’s hiking specialist, sheds light on the subject and gives you her best advice on how to dress well for any activity.

In this article, you’ll discover tips on how to choose the right base layer for any outdoor activity.

  1. What is a base layer?
  2. Three key elements for choosing a base layer
  3. The different materials for a base layer
  4. Merino wool density
  5. The fit of your base layer
  6. Did you know?

Base layers for menBase layers for women

1. What is a base layer?

A base layer is the first article of clothing you put on when you are layering. It usually consists of a long-sleeved shirt for the upper body and possibly leggings for the lower body. The base layer is followed by a mid-layer that you can add or remove depending on the weather, and a shell that will protect you from the elements (rain, snow, and wind). According to Fanny Bellerive, the base layer is probably the most important element of layering. It allows you to regulate body temperature and to wick away moisture during activities to stay dry, no matter the sport.

2. Three key elements for choosing a base layer

To choose your base layer, it is important to determine three things: the intensity of the activity you are going to do, the temperature of the day and your degree of perspiration and/or sensitivity to cold.

Determining the intensity of the activity

In winter, you don’t dress the same for an active cross-country ski trip as you do for a quiet afternoon of ice fishing. The more intense the activity, the more heat, and even moisture, it will generate. This is the case for cross-country skiing, alpine skiing, winter running, fat biking and, to a lesser extent, snowshoeing and ice skating, for example. You should therefore opt for a base layer that wicks perspiration very well and dries quickly.

On the other hand, when the activity is less intense or involves periods of inactivity, such as downhill skiing, hiking or ice fishing, it is important to keep the warmth close to the skin for as long as possible.

A base layer can also be an important part of your camping and travel kit, no matter what the season, as long as you need to stay warm and dry.

The temperature of the day

Of course, the weather factor also plays a role in the choice of your base layer. Before you dress for an activity, it’s a good idea to check not only the predicted temperature, but also the actual temperature, the wind factor and the humidex. The more polar the conditions (cold weather with wind or humidity for example), the more you will want to keep warm. You can then opt for a base layer like a long-sleeved sweater and long leggings to protect your thighs from the cold. Note that it is not recommended to layer several base layers. This will make it harder for moisture to escape. It is better to choose a thicker material (see the paragraph on merino wool densities below).

Though the base layer is often associated with winter, it is just as essential in spring when outside temperatures vary greatly. It can then be worn alone or with an insulating mid-layer and/or a soft shell.

Degree of perspiration and/or sensitivity to the cold

Are you the type of person who gets extremely cold and freezes right away as soon as you stand still for more than two minutes? Or, on the contrary, do you sweat at the slightest effort you make and your sweater gets soaked after a good climb? In both cases, a base layer is essential to help you manage your thermal needs (heat retention and breathability) and you can then play with the upper layers of clothing to adjust the temperature.

Once you’ve identified your needs, it’s important to consider the three most important factors of a good base layer: its materials, its density and its fit.

3. The different materials of a base layer

Merino wool

This natural and biodegradable fiber that comes straight from the backs of New Zealand sheep is the talk of the town when it comes to base layers. Among the advantages of merino wool are its thermoregulatory qualities, which means that it keeps you warm in winter and cool in summer. It also has anti-microbial and anti-odor properties, which are great for active multi-day trips like snowshoeing or cross-country skiing. It is also very soft, unlike other wools which sometimes irritate the skin. Of all the base layer materials, it is by far the warmest (depending on its density) and the most breathable. It is the material of choice for Icebreaker and Smartwool.

Synthetic materials

Synthetic fibers (polyester, nylon, polypropylene, etc.) are very good at wicking sweat and drying quickly. They can also be more economical than merino wool and more resistant to friction. There are different technologies, product qualities, brands and weights that exist. These can be an option for those who sweat a lot and feel that this option would keep them more comfortable.

Merino wool and synthetic blends

Some base layers are now made of a mixture of the two previous fibers and combine their qualities. This mix can be a very good compromise for those looking for versatility.

4. Merino wool density

If the main role of a base layer is, above all, to wick moisture from the body, it is important to choose the right thickness to obtain a good warmth/breathability ratio. To do this, you can compare the weight of the fabric per square meter, often simplified by a number from 120 (the lightest) to 320 (the warmest). Note that this applies only to merino wool garments.

Some examples:

  • 150: ideal for moderate to intense activities (such as hiking or cross-country skiing) on a mild spring day.
  • 250: ideal for low to moderate intensity activities (such as downhill skiing or ice fishing) on a very cold winter day.

5. The fit of your base layer

The closer your base layer is to your skin, the better it will wick away moisture and perspiration. During intense activity (cross-country skiing, fat biking, ski touring or snowshoeing), it is therefore important to choose clothing with a narrow or even tight fit.

Note also that men’s and women’s underwear are also important. They are also in contact with the skin and can be more or less breathable and warm. Several brands such as Icebreaker and Smartwool offer underwear made of merino wool.

6. Did you know?

  • For alpine skiing, it is recommended to wear short leggings (also called 3/4 leggings) with large socks as a base layer for the lower body. This avoids unnecessary pressure points between the two fabrics in the calf area, in the boot, and thus promotes better blood circulation.
  • Merino wool can absorb up to 30% of its weight in water before it feels damp against the skin, which promotes efficient evacuation of perspiration.
  • Naturally antimicrobial, merino wool does not retain odours and therefore does not need to be washed after each use. In fact, the less often you wash your merino socks, sweaters, base layers and underwear, the better they will wear.

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