Polymer compositions containing I) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (A) having an average particle diameter dso from 230 to 330 nm, II) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (B) having an average particle diameter d 50 from 340 to 480 nm, III) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (C) having an average particle diameter of 10 - 220 nm and IV) at least one rubber-free copolymer of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, characterized in that the butadiene polymer latices (A) and (B) were obtained by seeded polymerization using at least one butadiene polymer latex (C) having an average particle diameter of 10 to 220 nm as seed latex and the grafted rubber component III) was obtained by graft polymerization in the presence of at least one butadiene polymer latex (C) used as a seed latex for (A) and (B). I) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (A) having an average particle diameter dso from 230 to 330 nm, II) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (B) having an average particle diameter d 50 from 340 to 480 nm, III) at least one graft rubber polymer obtained by emulsion polymerization of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, in the presence of a butadiene polymer latex (C) having an average particle diameter of 10 - 220 nm and IV) at least one rubber-free copolymer of styrene and acrylonitrile in the weight ratio 95:5 to 50:50, wherein styrene and/or acrylonitrile may be wholly or partly replaced by α-methylstyrene, methyl methacrylate or N-phenylmaleimide or mixtures thereof, <EOS>