TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The method comprises dispersing the aqueous phase in the oil phase by homogenization to form a water-in-oil emulsion. The water-in-oil emulsion is coated on a substrate to form a liquid precursor porous organic polymeric film. The method further comprises removing the water from the aqueous phase droplets before or after removing the organic solvent from the oil phase of the liquid precursor porous organic polymeric film. Preferred Components: The oil phase further comprises: a low hydrophobic/lipophilic balance (HLB) emulsifier that is eventually disposed at the interface of the multiple discrete cavities and the continuous polymeric solid phase of the porous organic polymeric film; and a low HLB emulsifier that is an amphiphilic block copolymer that is eventually disposed at the interface of the multiple discrete cavities and the continuous polymeric solid phase of the porous organic polymeric film. The low HLB emulsifier is present at at least 1-100 wt.%, based on total oil phase weight. The amphiphilic block copolymer comprises a hydrophilic segment comprising polyethyleneoxide and an oleophilic segment comprising polycaprolactone. The cavity stabilizing hydrocolloid is carboxymethyl cellulose, a gelatin or gelatin derivative, a protein or protein derivative, a hydrophilic synthetic polymer, a water-soluble microgel, a polystyrene sulfonate, poly-2-acrylamido-2-methylpropane sulfonate, and/or a polyphosphonate. The cavity stabilizing hydrocolloid is present at at least 0.1-30 wt.%, preferably 0.1-20 wt.%, based on total aqueous phase weight. The solid porous organic polymeric film has an average dry thickness of at least 5-500 mu m, preferably at least 2-500 mu m. The water-insoluble polymer is a polyester, styrenic polymer, acrylic polymer, mono-olefin polymer, vinyl ester polymer, alpha -methylene aliphatic monocarboxylic acid ester polymer, vinyl ether polymer, vinyl ketone polymer and/or aliphatic cellulose ester polymer. The total volume of the multiple discrete cavities is a least 5-80%, based on total solid porous organic polymeric film dry volume. The multiple discrete cavities have an average size of at least 200 nm to 5 mu m. The organic solvent is ethyl acetate, propyl acetate, chloromethane, dicloromethane, vinyl chloride, trichloromethane, carbon tetrachloride, ethylene chloride, trichloroethane, toluene, xylene, cyclohexanone, dimethyl carbonate and/or 2-nitropropane. The polymer precursor is an ethylenically unsaturated polymerizable monomer including vinyl monomers and acrylic monomers. The water-insoluble polymer is a styrene-butyl acrylate copolymer, polycaprolactone, polyurethane, or bisphenol-A polyester. The porous organic polymeric film comprises first and second discrete cavities that are isolated from each other and dispersed within the continuous polymeric solid phase, where the first discrete cavities comprises a first marker material, and the second discrete cavities comprises a second marker material, which first and second marker materials are detectably different. The porous organic polymeric film is disposed on a substrate. The porous organic polymeric film has a reflectance of at least 6 times greater than a nonporous film composed of the same composition and dry thickness. In the porous organic polymeric film at least some of the multiple discrete cavities comprise an aqueous solution or suspension of an organic catalytic material or nanoparticles of catalytically active metallic materials, where the porous organic polymeric film is impermeable to the organic catalytic material and nanoparticles of catalytically active metallic materials, and the porous organic polymeric film is permeable to molecules having a molar mass of less than or equal to 1000 Daltons. The multiple discrete cavities comprise: the organic catalytic material that is an enzyme; or the nanoparticles of catalytically active metallic materials, where the nanoparticles comprise at least one element including groups 8, 9, 10 and 11 of the periodic table, and have an effective diameter of at least 1-200 nm. The porous organic polymeric film has an outer surface that has a contact angle with water that is at least 10 degrees greater than a solid nonporous organic polymeric film of the same composition and dry thickness. EXAMPLE - 30 g Poly(epsilon-caprolactone) and 20 g poly(ethylene oxide)-b-poly( epsilon -caprolactone) copolymers in ethyl acetate was mixed to give oil phase. 15 g solution of carboxymethyl cellulose was homogenized to give aqueous phase. The oil phase was homogenized with aqueous phase in a Microfluidizer (RTM: Homogenizer) to give a water-in-oil emulsion with water droplets of the size of 0.82 mu m. The resulting water-in-oil emulsion was coated onto substrate at a 0.01 cm wet lay down and dried under ambient conditions to yield a porous organic polymeric film.