<；P>；PROBLEM TO BE SOLVED: To provide a thin porous film excellent in moisture permeability and elasticity. <；P>；SOLUTION: A lamination type porous film is produced by laminating at least a layer A and a layer B. The layers A and B comprise resin compositions containing fillers in base resins, respectively. The base resins for the layers A and B are different from each other. When a sheet is formed from only each of the base resins for the layers A and B, at least one side of the sheet has a birefringence &Delta；n of <；0.9×；10<；SP>；-3<；/SP>；, when measured with an abbe refractometer according to JIS K7142, and the sheet has an air permeability of &le；2,000 sec/100 ml and a single tang tensile strength of &ge；2.0×；10<；SP>；-2<；/SP>；N. <；P>；COPYRIGHT: (C)2007,JPO&INPIT
