Roller covers are tools used in painting to apply paint evenly on surfaces. They consist of a cylindrical fabric cover that fits over a roller frame. The fabric absorbs paint and releases it onto walls, ceilings, or other surfaces, making the painting process faster and more efficient than using a brush. Different types of roller covers are available, designed for various surfaces and paint types. For example, nap length refers to the thickness of the fabric, which affects how much paint is applied. Choosing the right roller cover can help achieve a smooth finish and reduce the number of coats needed.