A polyolefin composition comprising, in percent by weight: A) 20-35% of a propylene homopolymer or copolymer with up to 8% of comonomer(s); B) 65-80% of a copolymer of ethylene and (i) propylene or (ii) CH2═CHR alpha-olefins, where R is a 2-8 carbon alkyl radical, or (iii) a combination thereof, optionally with minor amounts of a diene, containing from 40 to less than 54% of ethylene; wherein the weight ratio B/XS of the content B of copolymer component (B) to the fraction XS soluble in xylene at room temperature, both referred to the total weight of (A)+(B), is of 1.25 or less.