The silicone gasket inside the cap. It is what makes the bottle leak-proof, and it is the one part that ages.

If a bottle that used to travel lying down starts to weep, this is the fix. The seal is tested with sparkling water, the pressure case that finds a tired gasket first.

• Sized per bottle: 17 oz, 25 oz or 34 oz.
• Food-grade silicone, dishwasher safe.