Abstract: Method for retrofit improvement of the burglar-proofing of glass windows or glass doors, with the following process steps:Placing together of three films of which the two outer films consist of transparent plastic material and the inner of polyvinyl butyral (PVB) and/or polyurethane (PU), to form a three-layer ply.Heating of the PVB and/or PU (polyurethane) layer by thermal radiation before or after the placing together such that the film is placed in a plasticized state, at least on its outer face, and laminating the outer films with the inner film.Fabrication of a laminated sheet in the form of a transparent sandwich of the three films by the application of pressure and the allowing of the sandwich to cool.Joining of an existing glass pane in a glass door or glass window with a section of the laminated sheet, which is cut to the size of the glass pane and bonded to it.