FR-522, dibromoneopentyl glycol, a reactive flame retardant, contains 60% aliphatic bromine. Its high purity (FR-522 is typically 99% pure), is of benefit to the formulator. Thermosetting polyester resins can be formulated over a wide range of compositions to provide a broader selection of resin properties than those available with anhydride flame retardants. Resins formulated with FR-522 have high chemical and flame resistance, minimal thermal discoloration and excellent light stability. The high bromine content of FR-522 and its ready reaction into polyurethanes make it suitable for use in rigid polyurethane foams. It is increasingly used in CFC-free foam systems designed to meet more stringent standards of flame retardancy.