Went to 45K. I first tried it with a champagne glass but that did not
work, slipped around; can't have a concave bottom. I also tried
a glass exactly like the thin borosilicate glass in the vid but with
a thicker heavier glass bottom and that worked even better,
did not slide at all. Could have gone with that one but the thin
glass did okay, so left it. The glass height and water height are
success variables. Most important is a wide flat bottom. I'd
guess a plastic cup would be too lightweight, plus no risk.
Gotta have some risk to make it worthwhile. If your high wire
act has a net, why bother?