Silicone bands - these are reusable and meant to be put at the ends of sublimation tumblers to HELP avoid white spots at the end. Measure your tumbler to ensure fit (i have used on 20oz, 30oz skinnies, low balls and 12 oz skinny can koozies) - colors may vary
This is my process - put sub image on tumbler, tape as normal, put shrink wrap on and shrink it. Then put the silicone bands on the very end of the cups. Put in oven as usual. They will be hot when they come out of oven.