Baghouses are no longer new to the utility industry. As bags need to be replaced and the causes of bag failures determined, utility baghouse users have needed to learn more about fiberglass filter bag technology so they can write intelligent bid specifications, determine quality control procedures, and learn how to test new and used fiberglass filter fabrics. It has been found that no standard test methods exist to characterize new or used finished fiberglass fabrics used for filtration. The development of these standards for new finished fiberglass fabrics is urgently needed. The development of proper standard test methods for used fiberglass filtration fabrics is contingent on an understanding of the mechanisms which cause fiberglass filter media to fail while in service.