The Base layer is the first part of the three-layer system; this is the layer that deals with your sweat.
In order to make you more comfortable, this layer will move (or wick) the moisture away from your body to keep you warm, or even cool, during your activity.
Base layers will come in different styles and weights, using many different fabrics. Most are fairly light, worn for only wicking away sweat but some can be heavier, providing insolation for colder conditions. Some might even have windproof properties.
There are even those which will use natural fabrics, like Merino wool, which has a high warmth to weight ratio and great odour resistance.
Whether you wear your base layer beneath a long sleeved thermal mid-layer, a short sleeved cycling jersey or even beneath your outer layer, the base layer is a versatile piece for any cyclist’s wardrobe.