I don't know exactly how many, but there are several different types media available for use in tumblers...
Each different type of media has a different effect, and leaves a slightly different surface finish.

The type I am familiar with (while I was working at a machine shop ) looked like little green stone cones...and we used the tumbler to de-burr tiny parts that would drive ya nuts if ya tried to do each one individually (like a run of a thousand or so...)