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human
ELI5: How does wool or microfiber clothing draw moisture away from the body?

In the winter, I always wear a microfiber “fleece” jacket over a polo shirt and undershirt to work. Even in colder months, I tend to sweat profusely on my upper back, and it was very, very warm (80 degrees F) last week. Yesterday, I noticed that while the outside of the back of my jacket had a sheen of moisture on it, my polo shirt and undershirt were both almost completely dry. 

What causes the moisture to be drawn specifically to the outside of the material, rather than getting absorbed into it? My regular cotton shirts get soaked all the way through when I sweat, whereas with this fleece jacket only the outside was damp. Also, how did my other clothing also remain dry? I would have thought that since the undershirt and polo shirt were compressed against my skin they would have both been soaked, but they weren’t.
gpt
Microfiber - the actual individual fiber - is shaped like a straw and wants to fill itself up with moisture. So it is shaped to pull moisture away from the body into its straw. This also applies to other clothing. It pulls the water off your clothing and holds it. 

Wool is similar, but has a different structure. But it also expands and contracts to allow air flow or stop air flow depending on the temperature - remember that wool was once “alive” on an animal to protect it from the elements.