The present disclosure relates to a propylene ethylene 1-butene terpolymer wherein: (i) the content of ethylene derived units ranges from 1.1 wt % to 1.9 wt %, (ii) the content of 1-butene ranges from 5.0 wt % to 9.0 wt %, (iii) the melting point (Tm) of the non-nucleated terpolymer ranges from 125° C. to 137° C.; and (iv) the xylene soluble fraction at 25° C. is lower than 8.0 wt %.