Belegarth

I'm thinking about casting custom rocks out of stress ball foam. In the book of war it stats:
4.9.9. Class 5 weapons have a minimum diameter of four (4) inches (10.16 cm) and are constructed entirely of foam, cloth and/or tape (coreless).
My question is could a rock be solid foam without cloth or tape?

I don't see why not, though you'd want to make sure the raw foam isn't abrasive.