Porous film and a production method thereof

Good moisture permeability, for the purpose of vertical and horizontal strength balance has moisture permeability to provide a porous film and a production method thereof thinned with improved, the polyolefin resin 25 to 70 wt% and 75 to 30 wt% inorganic filler the resin composition film molding comprising a method for producing a resulting film porous film which opening extends 1.2 to 3 times in a direction perpendicular to the machine direction by a gear drawing process, and machine direction strength and the ratio between the intensity in the machine direction and perpendicular direction is 0.25 to 4.0, air permeability of 1000 sec / 100 cc or less, the moisture permeability of at least 2000g