I was open-minded enough to try these, but they are not the kind of filter discs you can buy at mushroom grow shops. These discs are rigid and will stay in place when you screw the lids onto the jars. These discs are flexible and have a soft texture, more like cloth than the Teflon material that other discs are made of. When I screw the lids onto my jars after sterilization, some of these filters twist under the lid and then buckle, allowing unfiltered air into my jars. With a different setting