A racquetball is made up of two components: an outer rubber shell and an inner core. The outer shell is constructed from a hard rubber material that helps it keep its shape while also providing an extra layer of protection against damage or punctures from sharp objects.  The inner core is usually composed of a lightweight material such as cork, foam, or plastic beads. This provides the necessary weight for the ball to achieve optimal bounce height when hit with a racket. Additionally, some manufacturers use air pockets within the inner core to increase overall lightness and promote a better game experience.