Process for producing a polypropylene composition by sequential polymerization comprising the steps: a) polymerizing in a first reactor, preferably a slurry reactor, monomers comprising propylene and optionally one or more comonomers selected from ethylene and C 4 -C 10 alpha-olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.8 wt%, and a MFR 2 in the range of from 15.0 to 40.0 g/10min, as measured according to ISO 1133 at 230 °C under a load of 2.16 kg b) polymerizing in a second reactor, preferably a first gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and C 4 -C 10 alpha-olefins, in the presence of the first propylene polymer fraction, to obtain a second propylene polymer fraction having a comonomer content in the range of 2.0 to 12.0 wt%, c) extruding the second propylene polymer fraction in the presence of at least one alpha-nucleating agent, wherein the polypropylene composition has an MFR2 in the range of from 15.0 to 60.0 g/10min, as measured according to ISO 1133 at 230 °C under a load of 2.16 kg and wherein the process is operated in the presence of a Ziegler-Natta catalyst with a transition metal of group 4 to 6 of the periodic table and the catalyst comprising an internal donor, optionally a co-catalyst and optionally an external donor, wherein the internal donor is a non-phthalic internal donor and wherein the non-phthalic internal donor is selected from (di)esters of non-phthalic carboxylic (di)acids wherein the (di)ester belongs to the group comprising malonates, maleates, citraconates, glutarates, cyclohexene-1,2-dicarboxylates and derivatives thereof or mixtures thereof. a) polymerizing in a first reactor, preferably a slurry reactor, monomers comprising propylene and optionally one or more comonomers selected from ethylene and C 4 -C 10 alpha-olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.8 wt%, and a MFR 2 in the range of from 15.0 to 40.0 g/10min, as measured according to ISO 1133 at 230 °C under a load of 2.16 kg b) polymerizing in a second reactor, preferably a first gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and C 4 -C 10 alpha-olefins, in the presence of the first propylene polymer fraction, to obtain a second propylene polymer fraction having a comonomer content in the range of 2.0 to 12.0 wt%, c) extruding the second propylene polymer fraction in the presence of at least one alpha-nucleating agent, wherein the polypropylene composition has an MFR2 in the range of from 15.0 to 60.0 g/10min, as measured according to ISO 1133 at 230 °C under a load of 2.16 kg and wherein the process is operated in the presence of a Ziegler-Natta catalyst with a transition metal of group 4 to 6 of the periodic table and the catalyst comprising an internal donor, optionally a co-catalyst and optionally an external donor, wherein the internal donor is a non-phthalic internal donor and wherein the non-phthalic internal donor is selected from (di)esters of non-phthalic carboxylic (di)acids wherein the (di)ester belongs to the group comprising malonates, maleates, citraconates, glutarates, cyclohexene-1,2-dicarboxylates and derivatives thereof or mixtures thereof.