What is a pinball ball made of?

Question

I figured it was metal, its just that it looks like rubber or something.

Answer 1

i would say rubber with a shiny coat  

Answer 2

i would says some kind of rubber material in the core and a metallic covering it

Answer 3

Highly-polished steel.

There are exceptions for special purpose situations, but 99+% of all pinballs are simply 1 & 1/16 inch diameter carbon steel.