A polyolefin composition comprising: A) from 85.0 wt % to 99.5 wt %; A terpolymer containing propylene, ethylene and 1-hexene wherein: (i) the content of 1-hexene derived units ranges from 1.0 wt % to 5.0%; (ii) the content of ethylene derived units is comprised between 0.5 wt % and 10.0 wt % (iii) the melting temperature ranges from 130° C. to 145° C.; B) from 0.5 wt % to 10.0 wt %; of a propylene, ethylene copolymer composition comprising: b1) from 12 wt % to 52 wt %; of a propylene homopolymer or a propylene/ethylene copolymer having a content of ethylene derived units ranging from 0.1 wt % to 4.5 wt %; and having a xylene soluble content measured at 25° C. lower than 10 wt %; b2) from 48 wt % to 88 wt % of a propylene ethylene copolymer having a content of ethylene derived units ranging from 15.0 wt % to wt % to 42.0 wt %; wherein the resulting polyolefin composition has an melt flow rate (230° C./5 kg. ISO 1133) ranging from 0.2 g/10 min to 4.0 g/10 min; the sum A+B being 100 and the sum b1+b2 being 100.