A heterogeneous in-situ polymer blend comprising a continuous phase comprising a polypropylene having a crystallinity of at least 30% and a melting point temperature Tm greater than 130° C., and a heat of fusion ΔHf greater than 65 J/g; and a dispersed phase comprising particles of an elastomeric copolymer dispersed in the continuous phase and having an average particle size of less than 5 micron, the elastomeric copolymer comprising ethylene units and 0.001 to 5 wt % diene by weight of the copolymer, and having a crystallinity of less than 20% and being at least partially cross-linked such that the degree of cross-link is at least 20%.