Abstract: A terpolymer containing propylene, ethylene and an alpha olefins of formula CH2?CHZ wherein Z is an hydrocarbon group having from 2 to 10 carbon atoms wherein: (i) the content of ethylene derived units ranges from 0.5 wt % to 5.0 wt %; (ii) the content of alpha olefin derived units ranges from 1.0 wt % to 5.0 wt %; (iii) the amount (Wt %) of alpha-olefin (C6), the amount (Wt %) of ethylene (C2) and the melting point (Tm) of the terpolymer fulfil the following relation (1) Tm>?(C2+0.8C6)*6+157 (1) (iv) the polydispersity index (P1) ranges from 3 to 8.