A roof liner is a type of material that is used to line the interior surface of a vehicle's roof. It can be made from various materials such as vinyl, cloth or leather and serves multiple purposes including providing insulation, sound deadening, and enhancing the appearance of the car's interior. The liner also helps protect the vehicle's original upholstery from wear and tear caused by items placed on the roof such as luggage, bicycles or other cargo. Overall, a roof liner is an important component that adds to the comfort and overall experience of driving a car.