An improved method of laminating a metal foil or sheet to a polyimide material is provided. A solution of a precursor of an intractable (i.e. thermosetting) polyimide is applied to a substrate and the solvent is removed to form a dry tack-free film. Thereafter, a solution of a precursor of a thermoplastic polyimide is applied onto the first film of polyimide and the solvent is removed to form a dry tack-free second film. Both films are then cured concomitantly at a sufficiently rapid rate and low temperature to effect substantial imidization of the polyimide precursors of both films without substantial crosslinking or densification of the polyimides in either of the films. Thereafter, a metal sheet or foil is laminated onto the thermoplastic polyimide film according to the following process. The thermoplastic film is contacted with the sheet or foil of metal to be laminated thereto. A first pressure is applied to the metal sheet and the polyimide substrate composite, which pressure is sufficiently low to permit outgassing of any gases trapped or generated within the polyimides and the temperature is increased. The temperature is raised to a level to essentially complete imidization of the polyimides and also to expel any gases contained or generated by said polyimide films. Thereafter, the pressure is increased to a second level or value and the temperature is controlled to a value which temperature is above the T.sub.g of the thermoplastic film. This second pressure is sufficiently high to complete the lamination of the metal sheet or foil to the thermoplastic polyimide.