Which fibre can do what?
How well a base layer meets the requirements - retaining heat and removing moisture - depends on the material and the processing of the individual fibres. Merino wool fibres are thirsty: they can absorb between 20 and 35 percent of their own weight in moisture, synthetic fibres only about 5 to 15 percent. This is why functional shirts made of merino wool feel dry for a long time when sweating. Once the absorption capacity is reached, however, every shirt feels wet to the skin - regardless of the type of fabric. But that is exactly what is supposed to be prevented. Let us look at the strengths and weaknesses of the materials processed in base layers:
1. Synthetic materials: They are usually made of polyester or polyester-polyamide blends. Although synthetic fibres absorb less water than wool, they are specialised in wicking moisture away from the body as quickly as possible via their surface (wicking effect). Due to the fast distribution, more moisture can be released to the outside, as a result functional shirts made of synthetic materials dry faster. They are somewhat lighter, more robust and more complex to process - and the raw material is cheaper. Their disadvantage: there are bacteria that love on our sweat, or better said the body fats and salts in it. Unfortunately, they can settle down quite well in synthetic materials. Their excretions - one can already guess at the word - cause bad smells. Bad for team sports or the social (or just not) sitting together during a ride break...
2. Wool fibres: Merino wool is used exclusively for direct skin contact, as it is significantly softer and finer than normal new wool. For comparison: On average, new wool has a thickness of 30-50 microns (1 micron = 0.001 millimetres), merino wool between 15-24 microns, a human hair between 50-100 microns. As described above, wool can absorb up to a third of its own volume of moisture without feeling wet. However, if the tanks are full, it takes correspondingly longer for the base layer to dry again. In addition, wool fibres are not as robust and abrasion-resistant as their synthetic counterparts. However, more and more base layer manufacturers are working with hybrid fibres in which merino wool fibres are wound around a core of nylon or polyester. This combines the strengths of both and deals with their weaknesses quite well. An enormous advantage of merino fibres is their ability to prevent the typical sports smell of sweat. Where this ability comes from has not yet been fully clarified, but it is assumed that the bacteria simply cannot attach themselves as well to the surface of the wool fibres. The result can be seen or smelled in any case - well in this case not.