Regular mouth size (90mm) cellulose filter discs made of 100% cellulose for mushroom cultivation. These cellulose filter discs are designed to take years of sterilization in an autoclave and can be reused many, many times. This price is per one synthetic filter disc. These Cellulose filter discs are designed to be used under a plastic lid with a 1/4" hole for gas exchange. A must have for the lab for grain to grain transfers and cultivating of mushroom spawn in jars.