The combination method of bubble pressure and fluid permeability was used to determine the average pore size and size distribution of a polypropylene(PP) microporous film prepared by biaxial stretching.The flux average pore size rJ and a parameter R90 = r90/rJ were suggested to characterize the pore structure of a microporous films

especially when they are used as filtration membranes. r90 is the pore size corresponding to 90% integral flux along the integral flux/pore size curve.The polypropylene microporous film sample shows a narrow pore size distribution with R90=1.26 and the average pore size rJ=14.9nm.