The present invention relates to a back-sheet comprising a weatherable layer, a structural layer and a functional layer whereby one of the layers comprises polybutylene terephthalate and one or both of the other layers comprises a polyolefin. The layer comprising polybutylene terephthalate preferably further comprises an impact modifier. The impact modifier comprises an elastomer that contains functional groups that bond chemically and/or interact physically with the polybutylene terephthalate and wherein the elastomer constitutes the dispersed phase at a concentration of 1-49 Vol %. Preferably the elastomer contains epoxy functional groups. The polyolefin is selected from the group consisting of polyethylene homo or copolymers, polypropylene homo or (block-)copolymers, cyclic olefin copolymers, polymethylpentene, a thermoplastic polyolefine (TPO), or blends thereof.