Pills are small knots or balls of mixture of large number of small fibers accumulated at the surface of the fabric and entangled by the mild frictional action during processing or wearing. They are soft but firmly held on the fabric create a fabric fault.
Mechanism of pilling: Pilling is a fabric surface fault characterized by little balls of entangled fiber clinging to the cloth surface. Pilling happens due to wearing of the surface. The surface of fabric when abraded the constituent fibers from the surface get liberated and becomes loose and further abrasion brings out entanglement on its surface.