Use a major paint manufacturers cup like PPG, Axalta/Cromax, BASF, etc. Those are known to be good. EZ-Mix is a known good brand as well. Stay away from buying cups on Amazon. And lesser known names. Stick to paint manufacturers cups you get at the paint jobber or EZ-Mix. Too many of the others have been mislabeled. Personally I like the Cromax cups that you can get at Axalta jobbers. They are 1 liter+ and they have a flat bottom as well.