To obtain a porous film which is excellent in chemical resistance and mechanical strengths, comprises thick-walled hollow yarns suitable for treating a high-viscosity liq., and has a high water permeability by forming a vinylidene fluoride resin film comprising hollow yarns and having a specified thickness and a specified relation between the bubble point and the water permeation rate (per unit thickness).

This film has a thickness of 0.5mm or higher, and when the bubble point (kgf/cm2) is 0.8, 1.1, or 3.4, then the amt. of permeated water is 4.3 or higher, 1.1 or higher, or 0.4 or higher, respectively. The film is dense, skinless, and isotropic, comprises a homogeneous network structure, and has an average pore size of 0.01μm or higher and a porosity of 50% or higher. The film is obtd. from a vinlydene fluoride homo- or copolymer, a homopolymer being pref., by thermally melting a mixture comprising the polymer, an org. liq., and an inorg. fine powder at a resin temp. of 235°C or higher, extruding the melt into hollow yarns, and causing the extrudate to run freely for at least 20cm.