The role of the base layer is to transport moisture in liquid form away from the skin.Base layer clothing is most often made of synthetic materials. Recently, natural Merino wool has been making a big comeback.The material is very pleasant and comfortable to wear.Compared to synthetic materials, wool wicks away sweat more slowly, but this is compensated by the fact that you don't feel cold even in a damp T-shirt.But for activities where you sweat a lot, thin synthetic materials are more suitable because they wick away sweat faster.
