The influence of binary mixtures of heptane with different diluents on the porous structure of styrene-divinylbenzene (Sty-DVB) copolymers was investigated. It was found that the porosity produced by the diluent mixtures depends not only on the affinity of each diluent for the copolymer but also on the interaction of the diluent molecules with themselves. In this work it was observed that some polar aromatic solvents when mixed with heptane presented cosolvency effects. In general, the accessible pore volumes were higher than the fixed pore ones, indicating the formation of elastic internuclear chains.