You Asked
How are bowling balls made? Doug, Calgary, Canada

Marshall Answered
Bowling balls are somewhat more complex than you might imagine. As described in the following video, they have a metal core, surrounded by resin, surrounded by polyurethane:

For more info on the core of a bowling ball see: How It’s Made: Bowling Ball Cores

This article describes the science of the surface materials used in bowling balls. There are “reactive resins” designed to have more grip on the lane, and particles mixed in with the polyurethane can create tiny spikes to give even more grip.

For more info see: How Bowling Pinsetters Work