Fun Factory Smartballs are made of new patented manufacturing process with a silent run feature that incorporates balls within silicone balls that make Smartballs the quietest love balls in the world. Inserted into the vagina, Smartballs can be worn for several hours. Every move you make causes the metal balls in the Smartballs' interior to vibrate, hence, the vaginal muscles are stimulated, massaged and exercised. Smartballs are made of safe, non-hazardous materials and a medical quality silicone coat. They come in a variety of colors and measure 1.5" around each. Smartballs are easily retrievable with a latex coated string.