Fibers comprising a polypropylene obtainable by a process comprising the steps of: (i) polymerizing propylene in the presence of a catalyst system comprising the product obtained by contacting the following components: (a) a solid catalyst component comprising a magnesium halide, a titanium compound having at least a Ti-halogen bond and at least two electron donor compounds one of which being present in an amount from 40 to 90% by mol with respect to the total amount of donors and selected from succinates and the other being selected from 1,3 diethers, (b) an aluminum hydrocarbyl compound, and (c) optionally an external electron donor compound, to obtain a polypropylene precursor having a melt flow rate MFR1; (ii) subjecting the thus-obtained polypropylene precursor to visbreaking to obtain a visbroken polypropylene having a melt flow rate MFR2; (iii) spinning the visbroken polypropylene obtained in the previous step; wherein MFR2 is comprised between from 15 to 40 g/10min, the ratio MFR2/MFR1 is comprised between 8 and 18, both MFR1 and MFR2 being measured according to ISO method 1133 (230° C, 2.16 kg).