polyethylene flexible pipe (1/2 inch or 1 inch)
You can make durable hoops (better than any available commercially) from flexible polyethylene pipe and a coupling (one per circle). These materials are available at hardware stores or plumbing supply houses.
Four feet of pipe makes a circle approximately 15 inches in diameter.
Six feet of pipe makes a circle approximately 23 inches in diameter.
Eight feet of pipe makes a circle approximately 30 inches in diameter.
2. Form the circle by joining the ends of the pipe with a coupling.
Helpful Hints Dipping the ends of the pipe in warm water may help the coupling slip in more easily. For small circles, use a hacksaw to saw 1/2" of each end of the coupling.