| Position | Against the skin |
| Job | Wick moisture, regulate temperature |
| Materials | Merino wool, synthetics (not cotton) |
| Part of | The layering system |
A base layer is the innermost clothing layer worn against the skin, designed to wick sweat away and keep you dry within the layering system. Made from merino wool or synthetics (not cotton), base layers regulate temperature and moisture; a dry base layer is the foundation of staying warm and comfortable outdoors.
Material matters
Merino wool or synthetics — both wick moisture; avoid cotton (‘cotton kills’) because it holds sweat and chills you.
In the system
It’s the first of the three layers, under the mid layer.
Frequently asked questions
What is a base layer?
A base layer is the layer worn next to your skin in a clothing system. Its job is to move (wick) sweat away from your body to the outer layers so it can evaporate, keeping your skin dry. Staying dry is what keeps you warm and comfortable as conditions and exertion change.
Should you choose merino or synthetic base layers?
Merino wool is naturally odor-resistant, warm even when damp, and comfortable across a wide temperature range, but dries slower and costs more. Synthetics wick and dry faster and are cheaper and more durable, but hold odor more. Many outdoor people own both for different conditions.
Why not wear cotton as a base layer?
Because cotton absorbs and holds sweat, staying wet against your skin and chilling you — the origin of the saying 'cotton kills'. A wet cotton base layer can lead to dangerous heat loss, so merino or synthetic base layers are strongly preferred outdoors.
Sources
- Layering basics — The Mountaineers