This part of ISO 3451 specifies methods for determination of the ash of poly(ethylene terephthalate), poly(butyleneterephthalate) and copolymers of the two, both filled and unfilled. The general procedures given in ISO 3451-1 arefollowed. For unfilled materials method A or method C of ISO 3451-1:1997 is used. For filled and glass-fibrereinforced materials method A of ISO 3451-1:1997 is used.For glass-fibre filled materials, containing flame retardant, antimony trioxide, and/or other, volatilizable additives, forinstance pigment zinc sulfide, a modification is incorporated to remove these as volatile bromine component(s).