I wish to make a large Newton's Cradle. That usually consists of five
suspended steel balls. Ideally the balls will be at least 2" in
diameter or up to 12" or 24" in diameter.
If they were steel they are likely to injure childen. So they can't be
steel. Billiard balls bounce well but are still too heavy.
Golf balls don't seem to bounce properly so they are no good, and are
too small. Soccer balls don't bounce that well either.
Polystyrene foam is too flimsy.

Any brilliant ideas? I have an idea which I will experiment with.