Sulfonated polymers are of interest for ion exchange resins, reaction supports, and membranes for separation, filtration, fuel cells, and electrochemical devices. Sulfonic groups have been introduced into polystyrene (PS) through exposure to sulfuric acid, and carbon nanotubes (CNTs) have been added to polymers to enhance proton conductivity without creating an electronic percolation pathway. PolyHIPEs, emulsion-templated porous polymers with highly interconnected hierarchical open-cell porous structures, are synthesized through polymerization in the external phases of high internal phase emulsions (HIPEs). In this article, the synthesis of PS-based CNT-filled polyHIPEs, their structure, sulfonation, and conductivity are described. Adding CNT dispersions to the HIPEs produced polymer nanoparticle-covered polyHIPEs from polymerization within the water-soluble surfactant micelles in the internal aqueous phase droplets. The CNTs migrated from the HIPE's aqueous phase droplets into the HIPE's organic phase and formed interconnected bundles within the polyHIPE walls, reflecting a reduction in the surfactant's ability to disperse the CNTs. The water adsorption in the hygroscopic sulfonated polyHIPEs increased the conductivity by several orders of magnitude. The conductivity of the sulfonated polyHIPE containing CNTs was more than an order of magnitude greater than that of the sulfonated polyHIPEs with no CNTs. The CNTs act as bridges, enhancing the connection between existing conductive pathways. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4369-4377