A stress ball is a malleable toy, usually not more than 7 cm in diameter. It is squeezed in the hand and manipulated by the fingers, ostensibly to either help relieve stress and muscle tension or to exercise the muscles of the hand.
There are many types of stress balls. Many are a closed-cell polyurethane foam rubber. This type of stress ball is made by injecting the liquid components of the foam into a mold. The resulting chemical reaction creates carbon dioxide bubbles as a byproduct, which in turn creates the foam.[1]
Stress balls, especially those used in physical therapy, can also contain gel of different densities inside a rubber or cloth skin. Another type uses a thin rubber membrane surrounding a fine powder. The latter type can be made at home by filling a balloon with baking soda. Some balls similar to a footbag are marketed and used as stress balls.
Despite the name, many stress balls are not spherical. Many stress toys are molded in amusing shapes and screen or transfer printed with corporate logos. They are presented to employees and clients as promotional gifts. Stress balls are the third most popular promotional gift in the UK. Stress toys are a staple of cubicles where repetitive stress injuries such as carpal tunnel syndrome are common. Because of the many shapes now available, stress balls are generically known as stress relievers.