During intensive activities, you can sweat a lot. Base layer clothing, also known as 'underlayer' or 'first layer', drains perspiration away to keep your skin dry and warm. Frequently used materials for this are synthetic, such as polyester or polypropylene. These fabrics hardly retain any moisture or odour. Another commonly used material is merino wool. Due to its natural moisture-regulating effect and its very fine structure, this type of wool feels good on the skin and is perfect as an underlayer.