This high quality Silicone Stopper gives a great airtight seal while still allowing gasses to escape.
Fits 3,5,6 & 6.5 Gallon glass carboys and 500ml flasks. This breathable Silicone Carboy Stopper acts as both a solid stopper and an airlock. The unique design allows CO2 pressure to escape but keeps oxygen and airborne contamination out. Beer makers love using it during the ferment because it creates a vacuum when the wort cools, instead of pulling water in from your traditional airlock. The airtight seal is great for extended lager fermentations when CO2 production is still present but only very slightly.
Measures 1 1/2" wide at the top and 1 1/8" at the bottom.