It depends on the manufacturer and whether the car seat has a high back or is backless. The structure of a high back seat may be metal or rigid plastic with energy absorbing foam padding surrounding the areas of the head and torso. A backless seat often includes a plastic base with foam padding to make it comfortable. The rest of the components are usually plastic to make the item lightweight. Not only is a high back seat with a metal frame heavier than one with a plastic frame, but they usually have longer service lives as well. Many companies that manufacture seats with metal frames give them a nine or 10-year expiration date from the time the customer buys it. The outside of the seat cover is usually a durable, washable material like polyester that parents can keep clean. On some seats, the cover or seat pad is removable and is machine washable. However, it's essential to read the manual to clean the booster seat correctly, so it still provides the protection a child needs when riding in a vehicle.