What is thermal underwear and how do you wear it properly?

In the past, thermal underwear was mainly worn as underwear in very cold countries. In recent years, however, thermal underwear has also established itself in outdoor sports and is part of the workwear for many. There is hardly an athlete left who does not have thermal underwear in his wardrobe. But what exactly is thermal underwear, what are they made of and how do you wear these special pieces correctly?

How does thermal underwear work?

Thermal underwear does not automatically make you warm. Rather, it is about the fact that thermal underwear, in comparison to other clothing, retains body temperature. It is quite normal to be a little chilly at the beginning of a workout in the fresh air. You first have to generate body heat through movement. If you are warm enough without moving, then you are wearing too much clothing. (Of course, this does not apply if it is 30 degrees outside.)

Thermal underwear not only retains body heat, but it also ensures that body moisture (sweat) is dissipated to the outside and that the item of clothing does not become saturated with sweat. Thermal wear also prevents rubbing on the skin. It lies on like a second skin and therefore does not rub against your body. Incidentally, thermal underwear is, depending on the fabric, not only ideal in winter, but can also ensure that you keep your body temperature cool in summer.

How do I wear thermal underwear?

Thermal underwear should be worn close to the skin and is therefore always the first layer of clothing – except for a sports bra. But that’s not enough. You should wear a long-sleeved functional shirt or turtleneck over it. When it is very cold or raining, you can also wear a jacket. That way you have three layers, which keep you warm.

The 3-layer principle

According to this principle – also known as the onion principle – three different layers of clothing of different thickness and material are worn on top of each other. The advantage of this clothing principle is based, among other things, on the fact that overall more air is stored as a heat insulator between the layers of clothing than with a few layers of thick clothing. This means that the body is better protected against the cold. The layers are:

• Sweat transport layer: This base layer of thermal underwear ensures that sweat is transported away and thus keeps the body dry.
• The insulation layer: This intermediate layer keeps the body warm, and wicks sweat away. It ideally consists of a (long-sleeved) functional shirt or turtleneck, but it can also be a fleece jacket.
• The weather protection: The third and top layer should protect against wind, rain or snow. If possible, it should be wind and waterproof.

Depending on the weather, you can of course get by with two layers. For example, if it is not raining and there is no wind, the third layer can be omitted. If it is very wet and windy but rather mild, you can leave out the second layer (insulation).