NOVELTY - Expandable polymer granule obtained from (a) polymer component comprising (a1) styrene copolymer component made of at least one styrene-acrylonitrile copolymer or a mixture of at least one styrene-acrylonitrile copolymer and at least one styrene-maleic acid anhydride copolymer and/or at least one styrene-acrylonitrile-maleic acid anhydride copolymers and (a2) at least one thermoplastic polymer, (b) a physical blowing agent component comprising at least one 2-7C hydrocarbon, and (c) a flame retardant system comprising at least one brominated trialkyl phosphate (I), is claimed.    USE - The expandable polymer granule is useful in a foam molded part, foam block or a composite molded part in furniture construction, construction industry, exhibition stand industry, automotive industry, boots- and ship building, wind power plants and/or thermal insulation (all claimed).    ADVANTAGE - The expandable polymer granule exhibits improved flame retardancy, improved compressive strength, improved flexural strength and improved bending energy.    DETAILED DESCRIPTION - Expandable polymer granule obtained from (a) 100 pts. wt. polymer component comprising (a1) 90-100 wt.% styrene copolymer component based on the polymer component, made of at least one styrene-acrylonitrile copolymer or a mixture of at least one styrene-acrylonitrile copolymer and at least one styrene-maleic acid anhydride copolymer and/or at least one styrene-acrylonitrile-maleic acid anhydride copolymers and (a2) 0-10 wt.% at least one thermoplastic polymer comprising aromatic polyethers, polyolefins, polyacrylates, polycarbonates, polyesters, polyamides, polysulfones, polyethersulfone, polyether ketones or polystyrene, based on the polymer component (b) 2-8 pts. wt. physical blowing agent component based the on polymer component, comprising 80-100 wt.% at least one 2-7C hydrocarbon based on the physical blowing agent component, and (c) a flame retardant system comprising 1-10 pts. wt. at least one brominated trialkyl phosphate of formula ((O)P(OR)3) (I) as a flame retardant based on the polymer component, is claimed.    R = optionally branched 1-6C alkyl, where at least one H is substituted with Br.    INDEPENDENT CLAIMS are also included for:    (1) producing the expandable polymer granule, comprising (a) providing the polymer component, (b) heating the polymer component to form a polymer melt, (c) introducing 2-8 wt.% physical blowing agent component based on the polymer component into the polymer melt to form a foamable melt, (d) homogenizing the mixture, (e) adding the flame retardant system and optionally further additives to the polymeric component in at least one of the steps (a)-(d), (f) extruding the blowing agent containing polymer melt through a die plate, and (g) granulating the blowing agent containing melt in a liquid-filled chamber under a pressure of 1-20 bar;    (2) producing a foam molded part, comprising producing the expandable polymer granules by the above mentioned method, prefoaming the granules to foam particles and welding the foam particles into a closed mold;    (3) the foam molded part or a foam block obtained from expandable polymer particles; and    (4) a composite molded part comprising a core material and at least one cover layer, where the core material is the foam molded part or the foam block.