i don't understand the strength difference between HDPE and PP. I make standard hoops out of pex 160psi pipe and irrigation black 100psi pipe. I find that if you make a hoop too big you lose it's rigidness. I worried this will happen with a larger polypro and I will be wasting my money. Does anyone have a larger polypro and can calm my worries????
You could always weigh it down with sand/water or something. They are collapsable, so you could add something to the inside. But I think it would be fine either way - 40 better than 42. I made a 46 once with extra hooping material (that one was color, so a bit stiffer material but relatively the same) and it was still pretty fun to play with (slow, of course, but still responsive).