AbstractComposite membranes are of interest for PEMFCs and DMFCs. This paper describes a basic study of the influence of silica on the proton conductivity: (i) added as a filler to poly(vinylidene fluoride‐hexafluoropropylene) and poly(benzimidazole)‐based membranes activated with H3PO4, or (ii) included in the matrix of class II hybrids based on tetraethoxysilane and poly(ethylene glycol) and activated with phosphotungstic acid (PWA).The addition of acidic silica as a filler determines proton conductivity increases up to one order of magnitude for filler amounts which strongly depend on the proton transport mechanism, and on the nature (free or partially free) of the activating acid. The increase of the silica content in the hybrid matrix induces a more complex behaviour which also depends on the amount of PWA.