NOVELTY - The production of a stripped porous polymer film from a heterogeneous porous polymer film which has surface characteristics that are different from the characteristics of the interior bulk material, comprises mechanically stripping a portion of a surface layer from the heterogeneous film.    USE - Stripped polymer film for use in e.g. liquid and gas filtration, waterproof breathable fabrics, controlled-release systems, batteries and fuel cells. The stripped polymer films can be used as: (i) membranes is filtration and ultra-filtration; (ii) proton exchange membranes in water electrolysis; (iii) composite membranes in chlor-alkali electrolysis; (iv) electrode separators in batteries; (v) ion-selective electrodes, particularly for use in the potentiometric determination of ions such as Ca2+, Na+ or K+; (vi) sensor materials for humidity sensors based on ion exchange membranes; (vii) ion exchange membranes for separations by ion exchange chromatography, e.g. de-ionization and desalination of water, ion separations, removal of interfering ionic species, and separation and purification of biomolecules; (viii) ion exchange membranes used in analytical pre-concentration techniques; (ix) ion exchange membranes in electrodialysis; (x) membranes in dialysis applications; (xi) membranes in gas separation and pervaporation; and (xii) bipolar membranes for use in water splitting and the recovery of acids and bases from waste water solutions.    ADVANTAGE - The surface characteristics of the stripped micro-porous polymer film more closely resemble the characteristics of the interior bulk material. The film exhibits improved permeability to and/or penetration of solids, liquids and gases, increased surface roughness, and increased average surface pore size, relative to the heterogeneous starting material from which it is prepared.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (i) a stripped porous polymer film with surface characteristics which are the same as the characteristics of the interior bulk material, in which the film comprises a polymer selected from polyethylene, polypropylene, polyvinylidene, polyvinylidene halides and copolymers of these;    (ii) a stripped porous film with surface characteristics which are the same as the characteristics of the interior bulk material, in which the film comprises a polyalkene and is made from a precursor film by forming a solution of the polyalkene into a film containing a solvent, cooling the film to below the gelling point of the solution, removing the solvent to yield a solvent-free film, and stretching the solvent-free film in at least one direction;    (iii) a membrane comprising a stripped porous film of (i);    (iv) a composite membrane comprising a stripped porous polymer film, which is at least partially filled with an ion exchange polymer, and where the stripped film is a micro-porous polymer film;    (v) a membrane electrode assembly comprising the composite membrane, where the membrane is an ion exchange membrane;    (vi) an electrochemical cell comprising the composite membrane, where the membrane is an ion exchange membrane; and    (vii) an electrochemical fuel cell comprising the composite membrane, where the membrane is an ion exchange membrane.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a reel-to-reel process used in the above method.    Porous polymer film (10)    Feed roller (12)    Collection roller (14)    Anchor (16)    Stripping roller (18)    Major surface (20)    Guide roller (22)    Second major surface (24)