ISO 3451-1-2008 "Determination of ash in plastics, Part 1: General methods" specifies methods for determining ash in polyethylene terephthalate, polybutylene terephthalate and their copolymers (filled and unfilled). This standard follows the general procedure in ISO 3451-1. For unfilled materials, Method A or Method C in ISO 3451-1:1997 can be used; for filled and fiberglass reinforced materials, Method A in ISO 3451-1:1997 is used. For materials containing flame retardants, antimony trioxide and Miscellaneous volatile additives, modification is required to remove these components. ISO 3451-1-2008 aims to provide accurate methods for ash determination for quality control of plastic products.