Abstract: A security token, such as a bank note or identity card, comprises a sheet-like substrate made up from film of transparent bi-axially oriented polymer coated with layers of opaque and heat activated adhesive material. The opaque layer is applied in such a way as to leave a transparent area for inspection of a security device, for example, a diffraction grating, incorporated in the polymer film. The substrate may bear printed or other identifying indicia and is protected with an intimately bonded layer of transparent polymeric material.