A process for producing an expandable pelletized polymeric material, comprising the steps of: a) providing a polymer component, consisting of PS) 90% to 99.9% by weight (based on P) of a styrene polymer component having a glass transition temperature of ≥ 130°C, formed from PS1) 30% to 100% by weight (based on P) of one or more styrene polymers comprising PS11) 60% to 85% by weight (based on PS1) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of alpha-methylstyrene and styrene, PS12) 15% to 40% by weight (based on PS1) of one or more than one polymerized monomer selected from the group consisting of maleic anhydride and maleimides and PS2) 0% to 70% by weight (based on P) of one or more styrene polymers other than PS1, comprising PS21) 60% to 82% by weight (based on PS2) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of styrene and alpha-methylstyrene, and PS22) 18% to 40% by weight (based on PS2) of polymerized acrylonitrile and PT) 0.1% to 10% by weight (based on P) of one or more thermoplastic polymers selected from the group consisting of aromatic polyethers; polyolefins; polyacrylates; polycarbonates; polyesters; polyamides; polyether sulfones; polyether ketones and polyether sulfides, (b) heating the polymer component to form a polymer melt, (c) introducing from 1% to 5% by weight (based on P) of a blowing agent component into the polymer melt to form a foamable melt, wherein C 3 -C 8, hydrocarbons and mixtures thereof are used as blowing agents, (d) homogenizing the mixture, (e) optionally adding additives to the P polymer component in one or more of steps a), b), c) and/or d), (f) extruding the blowing agent-containing polymer melt through a die plate, (g) pelletizing the blowing agent-containing melt in a liquid-filled chamber under a pressure of 1.5 to 15 bar to form a pelletized material. a) providing a polymer component, consisting of PS) 90% to 99.9% by weight (based on P) of a styrene polymer component having a glass transition temperature of ≥ 130°C, formed from PS1) 30% to 100% by weight (based on P) of one or more styrene polymers comprising PS11) 60% to 85% by weight (based on PS1) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of alpha-methylstyrene and styrene, PS12) 15% to 40% by weight (based on PS1) of one or more than one polymerized monomer selected from the group consisting of maleic anhydride and maleimides and PS2) 0% to 70% by weight (based on P) of one or more styrene polymers other than PS1, comprising PS21) 60% to 82% by weight (based on PS2) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of styrene and alpha-methylstyrene, and PS22) 18% to 40% by weight (based on PS2) of polymerized acrylonitrile and PT) 0.1% to 10% by weight (based on P) of one or more thermoplastic polymers selected from the group consisting of aromatic polyethers; polyolefins; polyacrylates; polycarbonates; polyesters; polyamides; polyether sulfones; polyether ketones and polyether sulfides, PS) 90% to 99.9% by weight (based on P) of a styrene polymer component having a glass transition temperature of ≥ 130°C, formed from PS1) 30% to 100% by weight (based on P) of one or more styrene polymers comprising PS11) 60% to 85% by weight (based on PS1) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of alpha-methylstyrene and styrene, PS12) 15% to 40% by weight (based on PS1) of one or more than one polymerized monomer selected from the group consisting of maleic anhydride and maleimides and PS2) 0% to 70% by weight (based on P) of one or more styrene polymers other than PS1, comprising PS21) 60% to 82% by weight (based on PS2) of polymerized styrene or alpha-methylstyrene or of a polymerized mixture of styrene and alpha-methylstyrene, and PS22) 18% to 40% by weight (based on PS2) of polymerized acrylonitrile and PT) 0.1% to 10% by weight (based on P) of one or more thermoplastic polymers selected from the group consisting of aromatic polyethers; polyolefins; polyacrylates; polycarbonates; polyesters; polyamides; polyether sulfones; polyether ketones and polyether sulfides, (b) heating the polymer component to form a polymer melt, (c) introducing from 1% to 5% by weight (based on P) of a blowing agent component into the polymer melt to form a foamable melt, wherein C 3 -C 8, hydrocarbons and mixtures thereof are used as blowing agents, (d) homogenizing the mixture, (e) optionally adding additives to the P polymer component in one or more of steps a), b), c) and/or d), (f) extruding the blowing agent-containing polymer melt through a die plate, (g) pelletizing the blowing agent-containing melt in a liquid-filled chamber under a pressure of 1.5 to 15 bar to form a pelletized material.