SLUB?

Slub cotton is a deliberate manipulation of an imperfection in the fabric in order to create a more textured effect on any given garment. When dyed, these imperfections bring out various fades and colors not normally found when dying a fabric that isn't slub. These imperfections come about after deliberately knotting or twisting the fabric as it is woven. The result is a garment that contains slight lumps and imperfections, often left in the fabric on purpose or created.