Selected substances are applied to the inner surface of the bubble during blown-film extrusion, with the intent of altering the physical, chemical or biological properties of resin films manufactured by the extrusion process. Preferred embodiments of the invention are disclosed, wherein a fluid preparation of selected substances is atomized from a point on the longitudinal axis of the bubble by one atomizing apparatus fixed on top of the die mandrel of a blown-film extruder. In the embodiments described, the atomizing apparatus is: (1) a tube that delivers fluid in a continuous manner to the center of the top surface of a spinning disc that atomizes the fluid towards the inner surface of the film bubble, or (2) a plurality of spraying nozzles connected to a tube that delivers the fluid to be atomized, and oriented to spray towards the inner surface of the film bubble.