Mini rollers are specially designed for painting smaller areas, while allowing you to eliminate the brush strokes created by the bristles on paint brushes. Mini paint rollers are most often available in 4-inch forms and come in a range of piles, which refer to the length of the material the roller sleeve is made from.In the construction industry, a roller refers to a heavy piece of machinery used to compact various materials such as soil, gravel, asphalt, and concrete. Its primary purpose is to create a stable, smooth, and durable surface by reducing air voids and increasing the material's density.