The invention relates to a method for the sterilization of the inside layer of a packaging material, the packaging material being produced as a laminate with an inside layer of a transparent thermoplastic which is applied on a reflective material layer. The sterilizing energy includes high energy light flashes emitted from one or more flash units, the light flashes being caused to act on the inside of the packaging material for purposes of exterminating bacteria and microorganisms present on the surface. Because the light flashes emitted from the flash unit are reflected by the reflective layer, the surface layer of the layer will be influenced by both the direct and the reflecting photoenergy from the flash units, the sterilizing effect being thereby improved. Packaging material well-suited for sterilization according to the method is also disclosed.