Bowling balls differ mainly between the coverstock and the core or also called weight block.  The coverstock is the outer shell of the ball or what we see. There are many types of materials used which determine the performance of each ball.  The core or weight block is the one that’s inside the outer shell or the coverstock. The weight and shape also determine the performance of the ball and the characteristics of each bowling ball are highly dependent on both the coverstock and the core.