Now I did it with the kids and it was amazing. You pour the powder in the mould, hold it underwater for a minute. Dry it in the mould for two minutes and open the mould and let it dry.
The end result was like the high-bouncer balls we used to play with as kids. (Lots of fun).
My question is: What is the chemical reaction in a home-made high-bouncer ball? (I'd also love a picture I can show my kids - but that is not essential).