NOVELTY - Preparing porous organic polymeric film, comprises: providing aqueous phase, and oil phase; dispersing aqueous phase in oil phase to form water-in-oil emulsion; applying water-in-oil emulsion to substrate; and removing organic solvent from oil phase and water from aqueous phase, and polymerizing polymer precursor if present, to form porous organic polymeric film comprising water insoluble polymer that provides continuous polymeric solid phase, and multiple discrete cavities having inner walls and that are uniformly dispersed within continuous polymeric solid phase.    USE - The method is useful for preparing porous organic polymeric film (claimed), which is used: in industrial, medical, optical applications; as catalytic surfaces and supports, adsorbents, chromatographic materials, membranes, lightweight structural materials, and thermal, acoustic and electrical insulators, and fuel cell membranes; in security systems for detection of counterfeits, document authentication, and labeling of consumer goods; in paper and plastic cards including driver's licenses, passports, and other identification cards; and as packaging and packaging components including fabrics, labels, polymeric films, fibers, tape, foils, paperstock, and cardboard packing.    ADVANTAGE - The method provides porous organic polymeric films using a single-step method.    DETAILED DESCRIPTION - Preparing a porous organic polymeric film, comprises: providing (a) an aqueous phase comprising a cavity stabilizing hydrocolloid, and (b) an oil phase comprising a water-insoluble polymer or polymer precursor and an organic solvent; dispersing the aqueous phase in the oil phase to form a water-in-oil emulsion; applying the water-in-oil emulsion to a substrate to form a wet coating containing droplets of the aqueous phase in the oil phase; and removing the organic solvent from the oil phase and water from the aqueous phase, and polymerizing the polymer precursor if present, to form a porous organic polymeric film comprising a water insoluble polymer that provides a continuous polymeric solid phase, and multiple discrete cavities having inner walls and that are uniformly dispersed within the continuous polymeric solid phase, where the porous organic polymeric film further comprises the cavity stabilizing hydrocolloid on the inner walls of the multiple discrete cavities.