BaseLayers – GearGuide


Super.Natural – BASE LS 175 gr – Mens Longsleeve

A good functional base layer is indispensable for every outdoor and action sports athlete. The importance of the effect of a good base layer cannot be understated and the effect is often times greater than that of a warm sweater or jacket as an additional outer layer. That is because this first layer makes sure that perspiration moisture is moved away from the skin.

Image: Under Armour ColdGear Fitted Crew Neck Base Layer

When your skin and underwear are wet – and stay wet – your body will cool down, making you feel uncomfortable and often plain miserable. When you get down and dirty in a cold environment, such as (tour)skiing, alpine climbing, or mountain biking, moisture-wicking undergarments are all but indispensable. Even with less intensive activities, such as hiking or camping out, a good base layer is the key to staying warm and comfortable by regulating your personal ecosystem.


  • Technology & Materials
  • Never wear cotton
  • When do you wear a baselayer?


Regardless of how mid layers and outer layers will change the base layer remains as indispensable as in the past. There are not that many variations in what a base layer is supposed to do. It is a very important and also a very basic product. That does not mean however that there this field has not continued to change and evolve, on the contrary!

Where functional base layers took off using synthetic fibers almost exclusively, the past years have seen the rise of natural products to such a degree that the balance has shifted to the use of the latter.

We have also seen a number of great examples where wool and polyester blends have been used. There is a growing variety of fiber compositions, structures, and thicknesses. You can pick and choose what product fits you and the activity you want to do.

At the same time, the designs and look of these functional base layers have improved so much that it can hardly be qualified as underwear anymore. If you decide to take off a mid or outer layer during a break, you don’t have to feel embarrassed anymore in your cool looking base layer (no pun intended).


The most widely used basic fibers are polypropylene, polyamide, polyester, and wool.

Natural fibers (wool and especially Merino wool):

Merino wool is the wool from Merino sheep. What makes it particularly good for clothing is that it is very soft and fine wool. Per square centimeter, a merino sheep will grow 10 times as many hairs than an average sheep. That means that it will a lot less itchy than those woolen sweaters your grandmother used to make you wear.

The insulating properties of wool are well known. But what is more important is that the material is breathable as well. That breathability is key to staying warm (not too warm) and comfortable. It allows for the natural process of transpiration, this is your body cooling down, but then just handles transpiration really well.

It is very good at transporting moisture away from the skin. The fibers actually absorb the moisture (they’re hydrophilic) and while the core of the fiber absorbs the moisture the surface remains dry. It can then release moisture to the open air, or next layer quite easily.

What is very special about wool is that it also makes sense to wear it in warmer weather. Wool will keep you warm when it is cold, and cool when it is warm. By helping your body transport the excess heat through transpiration as easily as possible away from your skin, it will in effect keep you cool.

Added to this is the anti-odor effect of wool. And that comes down to the structure of the wool fibers which is not unlike tiles on a roof, making it more difficult for bacteria to thrive on the fibers. Added to that, protein molecules in merino fibers, a.k.a. keratin break down odor forming bacteria.


Synthetic fibers (polyester and polyester blends):

Firstly, synthetic fibers, generally are really strong. It will be stronger than wool fibers. It will be resistant to most chemicals, it won’t stretch or shrink, hardly wrinkle, and it’s mildew resistant. Because the fibers are synthetic, it’s structure is very smooth and wearing polyester clothing is very comfortable.

Polyester is hydrophobic, meaning that it will repel water rather than absorb it. That means it will dry very quickly but can feel wet during heavy transpiration. It will be breathable and some new techniques in weaving structure help this as well.

Generally speaking, polyester products will be lower in weight, less expensive and can feel cooler to the skin in some circumstances than wool.

The wool that is used in products by, for example, Smartwool and Icebreaker is not only high quality (merino wool) but has also been treated so that the mentioned drawbacks (itchy and smelly) have disappeared completely. Sometimes the synthetic and natural materials are applied separately, knitted in a special way to enhance their specific properties.

Usually, they are combined with each other and/or with elastomeric fibers to use the benefits of each material. In other words, the different materials enhance each other’s properties and add additional features such as elasticity, heat insulation, and abrasion resistance. This also applies to the increasing variety of thicknesses and structures that are being applied. In this case, ‘thicker’ does not mean by definition ‘heavier’. Looser knitting that often looks bulkier make fabrics elastic and breathable. Inventive rib structures increase the surface area of the fabric so that perspiration moisture can spread more easily and wicked away from the body more easily.

Never wear cotton

A very important rule. Even though the feel of cotton is soft and comfortable it is useless for actions sports or intensive outdoor activities. For the simple reason, the base layer is directly in contact with your body. This also applies to socks and gloves, but because the base layer covers a large part of your skin, it is even more important to stay away from cotton when it comes to choosing a base layer.

Cotton is a wonderful material for everyday underwear, but as soon as you get active to this natural product is your biggest enemy. An important feature of cotton is that it absorbs moisture easily and then holds onto it; it dries very slowly. When you get physically active – not unusual in sports – cotton underwear absorbs all that transpiration, you’re wet and you stay wet.

And where those sticky wet clothes are annoying when you are active, they become even more horrible when you take the effort down a notch or take a break. Even at a pleasant outdoor temperature, your damp sweat causes cooling your skin down causes cold chills.

Needless to say, what will happen with a wet base layer in colder circumstances. From just feeling awfully cold to hypothermia is what you are in for. Bad for your muscles, joints and organs, detrimental to your energy level, and just a killer for any fun you’re having.

You will also notice that it takes a long time before your body is warmed up again when n you continue with your activity. And did we already mention how much energy is lost by this cooling down and warming up thing? So once again NO COTTON. You can have the most high-end midlayer and 600 euro 3-layer super shell jacket: but on a 10 euro cotton shirt and you’re screwed.

When do you wear a baselayer?

As mentioned, the rapid and adequate wicking of perspiration moisture is the main feature of a functional base layer. More so than purely keeping your body temperature up, as many people still believe. Therefore, the commonly used term ‘thermal underwear’ is actually inaccurate.

For the thermal insulation, technical base layers are of lesser significance and only provide real extra warmth in the somewhat thicker winter variants. This also explains why base layers are not only relevant when practicing outdoor and action sports in winter conditions, such as skiing, ice climbing, expeditions and snow shoe walking.

Even in warm weather, wearing functional underwear is highly recommended. Each specialized brand offers one or more series developed for specific weather conditions. Light, thin fabrics in a special composition and with an open structure guarantee a direct absorption of perspiration, followed by a rapid distribution over a large surface and an equally rapid evaporation to the open air.

This sums up the basic principle of functional underwear, regardless of thickness, material, and structure. Even when you would be able to practice your sport completely naked, from a purely functional point of view it is better to wear a base layer. A technical T-shirt is able to move sweat away from your body better than your body itself!