A propylene butylene polymer composition comprising A) a propylene butylene copolymer or a propylene butylene ethylene terpolymer which is—free of phthalic acid esters as well as decomposition products thereof; —obtained by a Ziegler-Natta catalyst and B) a mixture of at least one particulate and at least one soluble nucleating agent, whereby the propylene butylene polymer composition has—a MFR (2.16 kg/210° C.) in the range of 12 to 50 g/10 min—a tensile modulus (measured on injection moulded test specimens in accordance with ISO 527) of more than 1200 MPa—a Tm of more than 150° C.—an amount of xylene cold soluble (XCS) fraction of less than 7.0 wt.-% and whereby the propylene butylene copolymer includes monomer units derived from a) propylene in an amount of 91-96 wt.-% b) butylene in an amount of 4-9 wt.-% with respect to the total weight of the propylene butylene copolymer. or wherein the propylene butylene ethylene terpolymer includes monomer units derived from a) propylene in an amount of 90-96 wt.-% b) butylene in an amount of 4-9 wt.-% c) ethylene in an amount of not more than 1.0 wt.-% with respect to the total weight of the propylene butylene ethylene terpolymer.