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 different types of stress balls. Some are made from 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.