What is a stress ball? How does it work?

A stress ball is a malleable toy no bigger than 7cm in diameter.  Some stress relievers are made from closed-cell polyurethane foam rubber. These are 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. When you exercise pressure on a stress ball, the nerves and the muscles stimulate and contract, making them stronger. This, in turn, improves nervous system functioning and reduces essential hormones, which control and curb stress levels.