Thermal underwear

Thermal Underwear – the Base Layer That Decides How Warm You Stay

Thermal underwear is the layer in direct contact with your skin. Its job is to move sweat away and keep your body dry, because dry skin is warm skin. That is why good thermal underwear is the foundation of every outfit for skiing, winter hiking, ski touring, hunting and even cold days in the city.

In this category you will find men's and women's thermal underwear by Sensor (Czech Republic), Kilpi (Czech Republic), Husky (Czech Republic), Alpine Pro (Czech Republic) and the Bulgarian manufacturer Bars: tops, leggings and sets in synthetic fabrics and merino wool.

How to Choose Thermal Underwear

• Fabric: synthetic thermal underwear (polyester, polypropylene) dries quickly and is durable. Merino wool keeps you warm even when damp and naturally resists odours.
• Thickness and weight: thin base layers are for active movement and milder weather, while heavier ones (over 200 g/m²) are for cold and more static activities such as hunting or piste skiing.
• Fit: thermal underwear should sit close to the body without squeezing. Only then does it wick moisture effectively.
• Flat seams: they do not chafe under a backpack, hip belt or ski boots.
• Set or separate pieces: a long-sleeve top and leggings cover the whole body, while short-sleeve or sleeveless tops suit warmer days.

Synthetic or Merino – What Each Is Best For

Layering

Thermal underwear is the first of three layers. On top of it, wear a warm mid layer such as a fleece or a down jacket, and an outer jacket that protects from wind and water, for example a ski jacket. See also our subcategories men's thermal underwear, women's thermal underwear and merino thermal underwear.

Why Choose Extreme Sport

We have been equipping skiers and hikers for over 22 years and are the official importer of Kilpi and Husky for Bulgaria. Try the base layers on at our store at 42 Dondukov Blvd in Sofia, or order online with free delivery to an office or parcel locker over 50 EUR and 30 days for returns.

Frequently Asked Questions

What size thermal underwear should I choose?
Thermal underwear should fit snugly without squeezing or restricting movement. If you are between two sizes, choose the smaller one for active use and the larger one for more static activities.

How do I wash thermal underwear?
Wash synthetic base layers at 30–40 °C without fabric softener, as it clogs the fabric and reduces wicking. Wash merino on a gentle wool cycle up to 30 °C with a wool detergent and dry it flat.

Can I wear thermal underwear every day?
Yes. Thin base layers are comfortable under everyday clothes in winter, especially if you travel, work outdoors or spend long periods in the cold.

What thermal underwear is best for skiing?
For piste skiing choose a medium weight, and for very cold days or for children who spend a long time on the lift, a heavier model. A top and leggings set is the most practical choice.