Breathable plastic foam stopper replaces a stopper and airlock when making starters in your erlenmyer flask. Foam matrix allows for CO2/O2 exchange but is dense enough to keep bacteria out. Withstands boiling temperatures. Plug springs back to original shape after repeated use. Can also be used in place of a stopper and airlock on a carboy during fermentation.
Fits 2000ml and 5000ml erlenmeyer flasks.