Specific to this ball, there are two situations. One is a common practice ball in the arena, which is made of homogeneous plastic.
The other is a professional ball used by professional players. Let's have a look at this picture.
The dark gray part in the picture is the weight fortress of the ball. When making, the center of gravity can be adjusted to balance the quality of finger holes. You can also artificially create eccentricity to make the fairway more curved.
The light gray part is filled with resin to keep the shape of the ball.
The black part is rubber or synthetic rubber. Used to keep the texture of the ball surface and roll, slide and rotate on the fairway.
The red part is called the ball pin, and the surface of the ball will show the cross section. It is a red dot, indicating the direction of the center of gravity of the ball, which is convenient for judging the position when drilling the finger hole.
This is a bowling ball.