The influence of three N-substituted maleimides on the processing, thermal, and mechanical performance of high internal phase emulsion (HIPE) polymerized foams are investigated. N-propylmaleimide, N-butylmaleimide, and N-cyclohexylmaleimide were copolymerized with styrene and crosslinked with either divinylbenzene or bis(3-ethyl-5-methyl-4-maleimide-phenyl)methane in a HIPE polymerization process. The foam samples were evaluated by dynamic mechanical analysis, thermogravimetric analysis, compression strength measurements, and scanning electron microscopy. All maleimide modifiers produced increases in the foam glass transition temperature (T-g) as a function of the maleimide concentration. However, the degree of T-g improvement was strongly dependent on the N-substituted maleimide used during processing. Cyclohexylmaleimide produced higher T-g foams than propylmaleimide, which produced higher T-g foams than butylmaleimide. In addition, the N-substituted maleimide solubility in both the oil and water phases played important roles in the processing and final open-celled microstructure. The preferred N-substituted maleimide modifier should possess high solubility in the oil phase and insolubility in the water phase.