Sound waves travel fastest through a solid material. The second fastest medium is a liquid, and the slowest medium is a gas, because sound waves travel by vibrating molecules in a medium. In solids, these molecules are spaced closer together, causing sound to travel faster through it.
Gases, liquids and solids are three different types of matter or media through which sound can travel at different speeds. For example, the speed of sound through aluminum is approximately 17 times faster than through air at 40 degrees Celsius.
The speed of sound also varies in different types of solids, such as rubber and copper. The speed of sound of rubber is less than that of copper. This occurs because different materials have different densities and elastic properties. A material's elastic properties are related to how it can return to its original shape after deformation.