Abstract: Extruded, substantially closed-polystyrene foams that exhibit improved fire resistance yet contain lower levels of brominated fire retardant are disclosed. Methods of preparing the foams, comprising extruding the polystyrene with a novel fire retardant formulation comprising a mixture of a) a phosphate compound, preferably TPP; b) less than about 2.5 percent HBCD based on 100 percent polystyrene; and optionally c) a flow promoter such as dimethyldiphenylbutane, the extrusion process using a blowing agent which is preferably selected from carbon dioxide, mixtures of two or more of carbon dioxide, water, alcohol, ether and hydrocarbons, or a mixture of hydrofluorocarbons, alcohols, and hydrocarbons, are also disclosed. Use of the phosphate compound in the fire retardant formulation allows a reduction in the amount of brominated compound required and a reduction in the foaming temperature, resulting in lower density foams.