Thermoplastic polymer composition comprising: up to 99.75 wt.-% of at least one styrene-based polymer composition comprising at least one graft copolymer (A-1); 0.25 to 5 wt.-% of at least one organopolysiloxane compound; 0 to 10 wt.-% of at least one colorant, dye or pigment; and 0 to 3 wt.-% of at least one further additive; wherein the constituents to sum up to 100 wt.-% of the thermoplastic polymer composition; and wherein • the styrene-based polymer composition comprises 20 to 60 wt.-%, preferably 30 to 40 wt.-%, of at least one styrene-based graft copolymer (A-1) and 40 to 80 wt.-%, preferably 60 to 70 wt.-%, of at least one thermoplastic polymer (A-2) selected from poly(styrene-acrylonitrile), poly(a-methyl styrene-acrylonitrile) (AMSAN) and mixtures thereof; • the at least one organopolysiloxane compound has a weight average molecular weight Mw of 20,000 g/mol to 100,000 g/mol, determined by gel permeation chromatography relative to polystyrene as standard and THF as solvent; • wherein the at least one organopolysiloxane compound is a block copolymer comprising blocks of polysiloxane moieties comprising repeating units having the following formula (Ia): wherein each R 1 is independently selected from a linear or branched, saturated or unsaturated hydrocarbon group having 1 to 10, preferably 1 to 6, carbon atoms, and blocks of polyester and/or polyolefin moieties; and • the at least one graft copolymer (A-1) is selected from a poly(acrylonitrile-butadiene-styrene) having an average particle size D 50 of the rubber particles in the ABS copolymer from 50 to 750 nm, a poly(acrylonitrile-styrene-acrylic ester) having an average particle size D 50 of the rubber particles in the ASA copolymer from 50 to 1000 nm, and mixtures thereof, wherein the average particle size is determined using an ultracentrifuge. up to 99.75 wt.-% of at least one styrene-based polymer composition comprising at least one graft copolymer (A-1); 0.25 to 5 wt.-% of at least one organopolysiloxane compound; 0 to 10 wt.-% of at least one colorant, dye or pigment; and 0 to 3 wt.-% of at least one further additive; • the styrene-based polymer composition comprises 20 to 60 wt.-%, preferably 30 to 40 wt.-%, of at least one styrene-based graft copolymer (A-1) and 40 to 80 wt.-%, preferably 60 to 70 wt.-%, of at least one thermoplastic polymer (A-2) selected from poly(styrene-acrylonitrile), poly(a-methyl styrene-acrylonitrile) (AMSAN) and mixtures thereof; • the at least one organopolysiloxane compound has a weight average molecular weight Mw of 20,000 g/mol to 100,000 g/mol, determined by gel permeation chromatography relative to polystyrene as standard and THF as solvent; • wherein the at least one organopolysiloxane compound is a block copolymer comprising blocks of polysiloxane moieties comprising repeating units having the following formula (Ia): wherein each R 1 is independently selected from a linear or branched, saturated or unsaturated hydrocarbon group having 1 to 10, preferably 1 to 6, carbon atoms, and blocks of polyester and/or polyolefin moieties; and • the at least one graft copolymer (A-1) is selected from a poly(acrylonitrile-butadiene-styrene) having an average particle size D 50 of the rubber particles in the ABS copolymer from 50 to 750 nm, a poly(acrylonitrile-styrene-acrylic ester) having an average particle size D 50 of the rubber particles in the ASA copolymer from 50 to 1000 nm, and mixtures thereof, wherein the average particle size is determined using an ultracentrifuge.