This may be defined as the tendency of fibers to ball or roll up on the surface of a fabric. Pilling results when loose fiber ends escape from the yarn used in making a fabric and work their way to the surface of the fabric. After working the way to the surface of the fabric these loose ends begin to collect and wherever the fabric is exposed to rubbing, they form little balls of fuzz called pills. These unsightly pills are not at all new as they have always been fairly common on certain types of
woolen fabrics, particularly knitted fabrics. Their appearance in wool, however, was not nearly as serious as it is in fabrics made with some of the newer synthetic fibers. The pills that appear on wool fabrics will usually work their way out and be eliminated when the fabric is cleaned. This is not generally true, however, when these pills form on some of the synthetic fiber fabrics as the great strength of the synthetic fibers causes the pills to cling permanently to the surface of the fabric. Some of the many things that determine how well a finished fabric is going to resist pilling are as follows:

Staple length of the fibers used.
The amount of twist in the yarn.
The degree of sheering or singeing to which the fabric is subjected