Pilling, which describes small balls of fiber on a fabric, is something that can happen to almost any material. Pills form when short fibers in a material come loose, get tangled, and form tiny balls of yarn at the end of the fiber. The main cause of pilling is rubbing, which occurs most often during wear and in the wash. There are things you can do to prevent a fabric from pilling, but if you find that many of your garments pill, you can focus on materials that are less likely to have this problem.