Maximum sulfonation and minimum carboxylation are desirable in sulfonated styrene-divinylbenzene cation-exchange resins. These characteristics may be achieved with greater control of porosity of the base copolymers. Optimization of the porosity by varying both the nature and amount of porogen, and cross-linking for maximizing sulfonation and minimizing carboxylation, are reported. Predictors of the characteristics obtained by statistical analysis of the data, and the ranges of conditions in which they can be employed, are discussed. The optimum conditions are cross-linking 20% to 23% and pore volume 0.14 mL/g to 0.3 mL/g. The relationship of the particle size with porosity of the base copolymer and capacity of the resins is discussed. The effects of residual porogen/homopolymer on the sulfonation of these copolymers are also discussed.