A polyolefin compositions comprising: A) From 77 wt % to 90 wt %, of a propylene homopolymer having the fraction soluble in xylene at 25° C. lower than 2 wt %; B) from 10 wt % to 23 wt % of a copolymer of ethylene with one C4-C10 alpha-olefin containing from 20 wt % to 30 wt %, of said C4-C10 alpha-olefin derived units; said composition having the value of melt flow rate (MFR) at 230° C., 2.16 kg of from 0.5 to 4.5 g/10 min; the total content of ethylene of from 10 wt % to 18 wt %; the value of the intrinsic viscosity of the total fraction soluble in Xylene at 25° C. (AMXSIVtot) is less than 1.5 dl/g.