I was thinking of spraying that polyurethane foam that expands then hardens up inside a small hoop to give it a little more weight. Has anyone ever tried this? I'm going to try it on a $5 kids toy hoop first, and will post results. I'm a little worried that the foam won't be flexible enough, and with repeated use will crack up into chunks when the hoop gets stressed.
Well the foam will probably be mostly air and not add that much weight. Why don't you use water or rice instead?