What is in magnetic putty that makes it magnetic?

I have some magnetic putty- it’s a purple, stretchy, putty that came with a small magnet. The magnet is attracted to the putty and it’s a lot of fun to play with. I was wondering what is inside of the putty that makes the magnet stick to it. I was thinking that maybe they put small pieces of some sort of metal but then I think that would just separate from the putty to get to the magnet.