Better Bottle PET O-Ring Closure
Flexible stoppers and caps are the best solution for glass carboys, because glass carboys have irregular necks. Better-Bottle's PET O-ring rigid closure fits all sizes of Better-Bottle carboys and has none of the drawbacks of stoppers or caps. The closure is made of a special PET that can withstand continuous service at 100 C (212 F) and is hydrophobic and non-porous, so it does not stain or take up flavors and is easy to clean and sanitize.