Expanded styrenic polymers contain 1 to 20% by weight of one or more aromatic polyphosphonate compounds corresponding to the following structure I: wherein a and b are each from 0 to 6, with a+b being from 2 to 6, each R is independently hydrogen, unsubstituted or inertly substituted alkyl having up to 6 carbon atoms, —NO2, —NR12, —C≡N, —OR1, —C(O)OR1, or —C(O)NR12 (wherein R1 is hydrocarbyl or hydrogen), each R2 is independently hydrogen, alkyl or inertly substituted alkyl, each R3 is a covalent bond or a divalent linking group, and each R4 is independently an alkyl, aryl, inertly substituted alkyl or inertly substituted aryl group. The aromatic polyphosphonate compounds are effective FR additives for the expanded polymers.