A polymer film for laminating onto a metal substrate (M), the polymer film including an adhesion layer (A) and a bulk layer (B), wherein the adhesion layer is intended for bonding to the metal substrate and includes 20 to 50 wt. % of a non-crystallisable copolyester, 50 to 80 wt. % of polybutylene terephthalate (PBT) and 0-10 wt. % of polymers and additives, and wherein the bulk layer consists of is at least 91 wt. % of PBT and at most 9% of other polymers and additives.