A stress ball is a game soft, and usually not so big size in diameter. The pressure on the one hand, and manipulated by the fingers, it seems any help relieve stress and muscle tension or exercise hand muscles. There are many different types of stress balls. Some of polyurethane rubber made of closed-cell foam. The implementation of this type of stress ball by injecting liquid foam components in the template the resulting chemical reaction creates bubbles of carbon dioxide as a byproduct, which in turn creates foam and pu material stress balls available.
Stress balls, especially those used in physical therapy may also contain different bulk density within the skin, rubber or cloth. Another type uses a thin rubber membrane surrounding the fine powder. This could be the latter type are at home by filling a balloon with baking soda. Some similar balls foot bag marketed and used as stress