The density of the fiber determines the roller’s ability to hold paint and spread it evenly. Inexpensive rollers that become matted or fail to spread the paint will produce a mottled finish, regardless of the quality of paint used. They may also leave lint on the painted surface.
Mohair covers are especially good for applying enamel, while lambs wool covers are excellent for alkyd paints, but not latex.
Synthetic fibers make good all-purpose covers. In fact, about 95 percent of all roller covers are synthetic.
Smooth roller covers (with a 3/16″ or 1/4″ nap) are used for painting walls, floors and fine finishing.
Medium rollers covers (with a 3/8″ or 1/2″ nap) are used for for sand-textured walls.
Rough rollers covers (with a 3/4″ or 1″ nap) are used for light stucco walls and masonry floors.
Extra rough covers (with a 1-1/4″ nap) are used to paint brick, block, masonry and stucco.
Texture roller covers are designed specifically for the applying texture paints. Some are foam with patterns etched into the surface. Others have deep, looped material. Texture roller covers have large diameters to accommodate the heavier consistency of texture paints.