Abstract: A water-in-resin emulsion for producing a porous plastic is comprised of a mixture of water dispersed in discrete droplets uniformly throughout a continuous phase of a resinous copolymerizable composition which includes a copolymerizable mixture containing a liquid unsaturated polyester of a polyhydric alcohol and saturated and ethylenically unsaturated dicarboxylic acids and a compound having a polymerizable CH.sub.2 .dbd.C< group, wherein the copolymerizable mixture has a molecular weight in the range of from about 2500 to about 3500; a cobalt salt promoter in an amount within the range of from about 0.25 to about 0.5% based on the weight of the copolymerizable mixture; a tertiary aromatic amine accelerator in an amount within the range of from about 0.75 to about 1.75% based on the weight of the copolymerizable mixture; and, a lithium salt emulsifier in an amount within the range of from about 0.5 to about 1.5% based on the weight of the copolymerizable mixture.