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

Foam rubber

Foam rubber refers to rubber that has been manufactured with a foaming agent to create an air-filled matrix structure. Commercial foam rubbers are generally either polyurethane foam or natural foam rubber latex. Latex foam rubber, used in mattresses, is well-known for its endurance.-See also:*...

. 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.

Stress balls, especially those used in physical therapy

Physical therapy

Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and rehabilitation...

, can also contain gel

Gel

A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state...

 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

Footbag

A footbag is both a small, round bag, and the term for the various sports played with one – characterized by controlling the bag by using one's feet. Although often referred to generically as a Hacky Sack, that is the trademarked name of one specific brand.Footbag-like activities have existed...

 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 cubicle

Cubicle

Тhe cubicle, cubicle desk, office cubicle or cubicle workstation is a partially enclosed workspace, separated from neighboring workspaces by partitions that are usually tall...

s where repetitive stress injuries such as carpal tunnel syndrome

Carpal tunnel syndrome

Carpal Tunnel Syndrome is an entrapment idiopathic median neuropathy, causing paresthesia, pain, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. The pathophysiology is not completely understood but can be considered compression...

are common. Because of the many shapes now available, stress balls are generically known as stress relievers.