Patelai 30 oz Replacement Rubber Lid Seals Compatible Seals Lid Gaskets for 30 Oz Insulated Stainless Steel Tumblers Compatible with RTIC Atlin, Randomly Shipped in Oval and Round (White,6 Pieces)

Definitely won't leak. Not hard to put on, but so tight it hurts my thumb to push the lid off. Hopefully that will get easier. Much tighter than on a new cup. I had to pry the lid off with a spoon for a few days, but i did get easier. Still have a very good seal, but it's much easier to pop off with my thumb.

The Thermoflask's from Costco are my absolutely favorite water bottles. I was so bummed when I couldn't find a replacement silicone piece for it because mine was getting this black mildew on it that couldn't be washed after years of using it. I measured it and guessed that this would be the best fit for it and it fits so well. I'll definitely buy these again too extend the life of my favorite water bottle. Highly recommend.

These were advertised fit the 30 oz tumbler AND the 14 oz mugs. Perfect for the 30.oz tumbler. However, they are to big for the 14 oz mugs rendering them useless for the mugs. I really don't neeed 6 of these for my two tumblers and I'm thinking about returning them and trying a different brand or maybe I'll just keep them for future needs of replacements for the tumblers.

I bought the 30 oz Replacement Rubber Lid Seals to be able to replace them for our insulated water cups. I try to change them each time to keep them sanitary and clean. Mold can build up on those rings if you don't take them off and clean them and let them try completely.

Being white makes it easier to see if there is any mold hiding there. The only problem is they a just a little loose so when taking the lid off they tend to twist making it hard the put the lid back on. I’m now in the habit of untwisting them before trying to put the lid back on. I didn’t have that problem with the original gaskets