Mesoporous poly(styrene) (PS) containing various amounts of the cross-linker divinylbenzene was synthesized by a hard-templating routine using pressed pellets of fumed silica as templates. Porous polymers with a surface area of 215 m2 g−1 and porosities up to ∼35 vol % could be obtained. The impact of the cross-linker content and the processing on the porosity of the materials was investigated by nitrogen sorption and small-angle X-ray scattering. The surface area of the nascent porous PS increases and the pore size decreases with increasing amount of cross-linker. Furthermore, it was found that the porous polymers lose surface area at temperatures that are substantially below the glass transition temperature, Tg, of bulk polystyrene. The loss in surface area at temperatures below 65 °C suggests that partial pore collapse also may be induced in the glassy state. Finally, the stability of the mesopores against solvent swelling was investigated. A critical pore collapse was found at a cross-linker content of ∼20 wt %. In this context, also the existence of traced porosity, i.e., a nonaccessible mesostructure or porosity, could be confirmed.