The stainless steel is too slippery and the paint just runs off. Yes, I’ve had it happen, ugh! If you are only using paint, this is good practice so your mouth doesn’t touch the paint while you are drinking. Because I wanted to keep the stainless steel at the bottom uncovered, I masked it off first using blue masking tape, making sure to cover all of the bottom. Take small pieces and cover the bottom also. This is extremely important if you are selling cups or will ever (even maybe) drink without a straw. There are a lot of different options on how to paint a yeti cup or ozark tumbler and I have tried many! case. in. I’ve read a lot about having to sand the cup because the paint won’t stick and that is true with a lot of paints. Apply the tape to the bottom ridge of the cup also. If you are going to epoxy the tumbler, this also helps prevent the resin from cracking if dropped. Before painting, I had to prepare the tumbler in order to get the best results that I could. I use a straw daily but used the tape just. Apply painters tape around the top rim of the cup. Before you spray paint stainless steel tumblers, you’ll need to tape off the top with painter’s tape or electrical paint.