The invention is a flame retardant for styrene foams. The flame retardant contains both aromatic bromine and an olefin. The olefin is an internal olefin. Desirable flame retardants are selected from:formula I: wherein R1 is C1-C6 and optionally containing a heteroatom or olefin; R2 is C1-C6 and optionally containing a heteroatom or olefin; and R3-R12 is H, C1-C6 (optionally containing a heteroatom), or halogen; and further wherein the compound of formula I is present in a concentration of at least 50 percent of a trans isomer; formula II: wherein R1 is Halogen, C1-C6 and optionally containing a heteroatom or olefin; R2 is Halogen, C1-C6 and optionally containing a heteroatom or olefin; and R3-R7 is H, C1-C6 (optionally containing a heteroatom), or halogen; and formula III: wherein R1 is Halogen, C1-C6 and optionally containing a heteroatom or olefin; R2 is Halogen, H, C1-C6 and optionally containing a heteroatom or olefin; and R3-R6 is H, halogen.