What is the billard ...

Question

cue ball made of ?

Answer 1

Most pool balls today are made of phenolic resin. This includes the cue ball. They have been made of several different materials over the years but phenolic resin is the norm for today.  

Answer 2

long ago they were made of ivory...

but now..

man made polymer which is:

a compound of high molecular weight derived either by the addition of many smaller molecules, as polyethylene, or by the condensation of many smaller molecules with the elimination of water, alcohol, or the like, as nylon.