The Hammer Tough is not like other spare balls. This ball introduces the Polythane coverstock and wraps it around a pancake core. The Hammer Tough is the toughest spare ball to be created so far. Carbon Fiber Infused! Carbon fiber is one of the toughest materials on earth. Hammer decided to add this material to the inner core of this ball for added strength and durability allowing them to offer an incredible 3 year warranty.