The vented silicone stopper does the job of both a stopper and an airlock and fits most carboys greater than 3 gallons. There are 4 vents with a pliable seal that will open to let CO2 escape as it builds, but close instantly once the pressure is released. This prevents contamination by airborne pathogens. You no longer have to worry about liquid from the airlock spilling into your fermenting beer.
