Merino wool running base layer: why and how to adopt it for cold-weather running
As soon as the thermometer drops, a question comes up every autumn: what should you wear under your jacket to run in the cold without overheating or shivering? The answer often comes down to one word: merino. Season after season, this fine wool remains the reference material for the base layer of runners who head out in cool weather.
Why merino wool remains the standard for cold weather
Unlike cotton, which retains moisture and cools the skin as soon as it gets wet, merino keeps its insulating properties even when damp. Its fiber is naturally thermoregulatory: it retains body heat in cold weather while wicking sweat away during exercise. The result is that you don't finish your run soaked or freezing.
Merino also has a practical advantage that is too often underestimated: it is naturally odor-resistant. Its fibrous structure limits the development of bacteria responsible for unpleasant smells, which means fewer washes and a garment that lasts longer.
Merino and recycled polyester: the technical compromise
Used on its own, merino wool has one limitation: it dries less quickly than synthetic fibers and can lack the elasticity required for a close-fitting garment. That is why recent running base layers, like our Serena long-sleeve, combine merino with recycled polyester. This blend retains the thermoregulating and anti-odor qualities of wool while gaining stretch, lightness, and quick-drying properties—a technical compromise designed to support running and trail sessions in cool to cold weather.
How to properly wear your running base layer
The base layer should always be worn in direct contact with the skin, never over another garment. It is responsible for managing sweat wicking, a function it cannot perform if it is not in contact with the skin.
For very cold outings, you can then layer a second insulating layer (such as a tank top or technical t-shirt) and, if necessary, a windproof or waterproof outer layer. A well-chosen merino base layer is often sufficient on its own in cool weather, making it a versatile piece even outside of running.
Care: merino wool is not washed like synthetic fiber
Unlike 100% synthetic fibers, merino wool requires some specific precautions to avoid damage:
Cold wash, wool or delicate cycle. 30°C maximum, never more. Heat will irreversibly felt the wool fiber, causing it to shrink and lose its softness.
No vigorous spin cycles. A short spin at low speed is sufficient. Spinning too hard deforms the fibers, causing the garment to lose its fit.
Dry flat, never in a tumble dryer. The heat from a tumble dryer felts wool in the same way as washing it at too high a temperature. Lay the garment flat, away from direct heat sources.
No fabric softener. As with technical synthetic fibers, fabric softener leaves a film that blocks the fiber's natural properties. It is unnecessary for merino wool, which is naturally soft.
Wash less often. This is one of the great advantages of merino: thanks to its natural resistance to odors, a base layer can be worn several times between washes. A simple airing out is often enough after a short run.
In summary
Season after season, merino remains the most reliable material for running in the cold: it keeps you warm without overheating, remains effective even when damp, and is naturally odor-resistant. Combined with recycled polyester for added technical performance, it is the foundation of a well-thought-out autumn and winter running wardrobe.
→ Discover the Serena long-sleeve base layer in Graphite or in Granite, made from merino and recycled polyester, in the Spiridon shop.
Franck Tuil - Author - Running culture specialist