Synthetic Filter Discs are used by many mushroom cultivators. From those only using a few jars of spawn to act as spawn masters in commercial production, to those involved in smaller home cultivation. These synthetic filters discs fit precisely on a variety of canning jars that are commonly used by toady's cultivators. Usage of these discs allows a fresh, constant air exchange but prevents the entrance of unwanted contaminates. Sterilizable and reusable for life (not for food canning) 99.97% efficient filtration down to .3 microns.