Abstract: The invention concerns a method for producing a microporous film with strong isotropic tendency permeable to gases and impermeable to aqueous liquids, consisting of at least one layer, comprising the following successive steps: preparing a mixture consisting of a polyolefin matrix containing at least a polymer and at least a mineral and/or organic filler; extruding at least a ply by hot-casting the mixture; pre-stretching the ply with a drag roll; cooling and solidifying the pre-stretched ply, using the drag roll; drawing the solidified ply at sufficient temperature for forming the microporous film.