A method for producing a non-breathable micro-porous thermoplastic polymer film for outer covering of diapers and sanitary towels includes a dispersion step by mixture of mineral particles surface-covered with a hydrophobic layer of fatty acid, a base polymer and a co-polymer adhesive, wherein the co-polymer adhesive is selected to comprise the base polymer; and film forming step in a film extrusion line having a flat film extruder provided with an extrusion nozzle, wherein the mixture is fed to the flat film extruder forming the film, and hot stretching the film between the extrusion nozzle and the solidification of the formed film, thereby obtaining the non-breathable micro-porous film with pores sizing from 0.5 to 5 μm without communication between the pores. The process requires less raw materials with a further reduction of film thickness, while giving a matt appearance to the film, thus making the usual micro-embossing step of the extrusion line unnecessary.