A breathable Silicone stopper that acts as both a stopper and an airlock. Unique design allows CO2 pressure to escape but keeps Oxygen and airborne contamination out. This quickly became our stopper of choice for wine, and is a popular style used by numerous commercial wineries. Also has great application for beer ferments: It will create a vacuum if fermenting wort cools (as opposed to pulling water in from your traditional airlock.) Airtight seal is great for extended fermented lager when CO2 production is still present but very slight. 

• Fits 3, 5, 6 & 6.5 gallon glass carboys, 1 gallon bottles, growlers, and 500 mL flasks.
• Replaces Stopper Sizes #6, #6.5, #7, #8
• Stopper Measurements: 0.94" x 1.48" (24 mm x 37.5 mm)
• The flapper stopper protrudes roughly 2.5" from the stopper to allow for easy assembly

Other available sizes include the Universal Breathable Bung and the Breathable Barrel Bung. All three size options can be purchased in one complete bundle with the Breather Bung Pack.