Fabric Defects 101- Understanding Overcoming Pilling 

Pills are defined as small balls of entangled fibers that are attached on the surface of a fabric or material
Pilling Resistance is the measurement of the tendency of a material or fabric to form pills on its surface
Anchor Fibers
The pills shown here have long, strong anchor fibers (polyester) which are holding entangled balls of loose fiber to the surface. The anchors are pulled from the surface of the fabric during use and have captured the loose lint during wear and laundering. The anchor fibers also entangle with other anchors fibers to also form pills.