The Base Layer is worn next to the skin not just for winter, it is equally effective in warmer conditions as well. Moisture Management is a main function for this primary layer; to assist in the removal of moisture from the skin. This layer should be close fitting with high stretch qualities.
An insulation layer should not be next to the skin, as it will ‘choke’ the key element of wicking perspiration. So in winter, a membrane garment should not touch the skin – a long sleeve base layer should be the first contact. This winter garment should still be thin to permit the moisture transfer to occur. The thermal protection of the rider should be carried out by the mid layer or jacket.
Even in summer, on all but the hottest days your Base Layer should wick moisture away from the skin to the outside of the garment where it evaporates quickly to give a cooling effect on the body. If you dress correctly, the temperature between the body and base layer should be the same all year round.Summer base layers should be super light with minimal seams and labels. Over 25 degrees, ultra light summer jerseys with their own wicking properties can stand alone unless they become saturated and sit wet on the skin providing a cold thermal bridge to the chest, unwanted on long descents.
No evidence to prove the following; but in racing I always wore two layers in summer . Better riders than me stated the base garment provided a ‘slide’ layer with the jersey and extra protection in crashes.
