Foam rubber is a type of synthetic rubber that is made by whipping air into a rubber compound. This creates a material that is lightweight, flexible, and has excellent sound-absorbing properties. Foam rubber is often used in a variety of applications where sound absorption is important, such as in car interiors, furniture, and recording studios.
Cotton and leather are both natural materials that are not as effective at absorbing sound as foam rubber. Cotton is a fibrous material that allows sound waves to pass through it easily. Leather is a dense material that reflects sound waves back into the room.