Always wondered. I bet it's about fifteen cents worth of plastic.

 

It is a synthetic version of the same stuff kids play with.
A mildly abrasive polymer.

 

Thanks. I thought it resembled Silly Putty. Why doesn't anyone mass-produce it and undersell everyone else, I wonder? $8 for a tiny piece is absurd. Or maybe someone does?

 

Kaolin (a certain type of refined clay). Along with some fillers and materials to keep it from dissolving too quickly.

Better known for its role in Kao-Pectate although they appear to have changed their formula and now it's just like Pepto Bismol.

There are also synthetic "clays" used; I don't know what those are.

 

Here's a great deal: A pound and a quarter for $17.

Edit: Oops! It's only 4 oz.

 

Oh; and here's one you can use with an orbital buffer. (Scroll all the way down.) Who knew?