A polyolefin composition comprising: A) from 65 wt % to 85 wt %, of a propylene/ethylene/1-butene terpolymer wherein: i) the content of ethylene derived units ranges from 0.6 wt % to 2.5 wt; ii) the content of 1-butene derived units ranges from 6 wt % to 12 wt %; iii) the fraction soluble in xylene at 25° C. ranges from 3.5 wt % to 20 wt %; B) from 15 wt % to 35 wt % of a propylene/ethylene copolymer having a content of ethylene derived units ranging from 10 wt % to 40 wt %; the copolymer optionally can contains 1-butene derived units in an amount less than 1 wt %; the sum A)+B) being 100.