Paper pilling happens when the fibers of the paper surface become damaged. The fibers loosen from the surface of the paper and gather into small, raised clumps, balls, or rolled strings.
Paper pilling is caused by excessive pressure, repeated rubbing, erasing, or damaging the paper structure with solvents— anything that breaks down the integrity of the paper. Papers with weaker surface strength, office grade papers, handmade paper, and cold pressed watercolor paper are more susceptible to pilling.
Unlike pigment pilling, which involves clumping colored pencil material, paper pilling is physical damage to the paper itself.
Once paper begins to pill, the damaged area becomes rough, uneven, or difficult to color smoothly. For colored pencils, you can visibly see where someone has colored over a damaged area.
Paper pilling is irreversible because the original surface texture has been disrupted.