Wool trousers are made of wool thread. It won't knot.

Sandwich trousers are cotton trousers made of wool like cotton. But after a long time, you will have a knot and need to take care of it again.

Wool is mainly composed of protein. The use of wool by human beings can be traced back to the Neolithic Age and spread from Central Asia to the Mediterranean and other parts of the world, thus becoming the main textile raw material in Asia and Europe.