Polyolefin compositions comprising (percent by weight) A) 60%-95% of a crystalline polypropylene component having a Melt Flow Rate (MFRA) value of from 2.5 to 50 g/10 min. and containing from 20% to 80% of a fraction AI) having MFRI from 0.5 to 8 g/10 min., and from 20% to 80% of a fraction AII); B) 5%-40% of a copolymer of ethylene with one or more C4-C10 &agr;-olefin(s) containing from 10 to 40% of said C4-C10 &agr;-olefin(s); the ratio MFRA/MFRI being from 2 to 25; the percentages of A) and B) being referred to the sum of A) and B), and the percentages of AI) and AII) being referred to the sun of AI) and AII).