Well I thought that I had cleaned out my two synthetic cone filters and allowed them to dry before putting in a plastic bag and then in an enclosed storage area in the sugarhouse. When I went today to check to see how many prefilters I had, much to my suprise both of my cone filters are spotted with mold and one even has multiple colors on it. So I do not know whether these should just be tossed out or if I can boil them and still be able to use them?