A roller cover is a type of painting tool designed to apply paint evenly on surfaces. It consists of a cylindrical fabric cover that fits over a roller frame. The cover absorbs paint and allows for smooth application on walls, ceilings, and other large areas, making it a popular choice for both professional painters and DIY enthusiasts. Roller covers come in various materials and nap lengths, which determine the texture and finish of the paint job. Common materials include synthetic fibers and natural fibers, while nap lengths can range from short to long, depending on the surface being painted, such as smooth drywall or rough concrete.