'PolyHIPE' are porous polymers from the polymerization of monomers and crosslinking co-monomers in the continuous phase of high internal phase emulsions (HIPE). Elastomeric polyHIPE have been reinforced through the synthesis of nanocomposites using several different routes including the addition of co-monomers such as vinyltrialkoxysilane, polyhedral oligomeric silsesquioxane (POSS) bearing vinyl groups, or vinyl silsesquioxane (VSQ). This paper describes the synthesis, structure, and properties of hybrid polyHIPE with interpenetrating polymer-inorganic networks synthesized by adding tetraethylorthosilicate (TEOS) to the monomers. The HIPE becomes unstable on addition of 14 mol% TEOS and the resulting polyHIPE contains voids hundreds of micrometers in diameter. On addition of 25 mol% TEOS the large voids become coated with a brittle Si-O shell as the TEOS migrates to the interface between the organic and aqueous phases. In general, the increases in tan 5 peak temperature, tan 6 peak breadth, and room temperature modulus with increasing TEOS content are similar to those observed with POSS and VSQ. Unlike the polyHIPE containing vinyltrialkoxysilane, POSS, or VSQ, pyrolysis of these hybrid polyHIPE did not yield porous inorganic monoliths. (C) 2007 Elsevier Ltd. All rights reserved.