Breathable Silicon Rubber Stopper

Our Silicone Stopper provides an airtight seal while still allowing gasses to escape, no need for an airlock! Fits 3,5,6 & 6.5 Gallon glass carboys and 500ml flasks. Can be used as either a solid stopper or an airlock. 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. Also, a great option 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.