Gels of amorphous and alpha-layered Zr(HPO4)(1.0)(O3PC6H4SO3H)(1.0), hereafter Zr(SPP), in DMF were used to prepare composite proton conducting membranes based on polyvinylidene fluoride (PVDF) with Zr(SPP) loading from 5 to 25 wt.%. The membranes prepared with alpha-Zr(SPP) are less compact and homogeneous than those obtained with the amorphous filler. In the latter membranes, the size of the filler particles, determined by TEM microscopy, is in the range of 10-20 nm. Proton conductivity and water content of the membranes made of amorphous Zr(SPP) were determined as a function of temperature from 80 to 130 degrees C, at 90% RH, and as a function of RH, at 100 degrees C. In all cases the conductivity is nearly constant up to 120 degrees C and decreases irreversibly at higher temperatures. With increasing filler loading up to 25 wt.%, the conductivity increases by a factor of 30 and reaches 2 center dot 10(-3) S/cm, at 120 degrees C and 90% RH; under these conditions, the H2O/SO3H molar ratio is 8.5. Moreover, in the RH range 60-90%, H2O/SO3H increases with RH from 5 to 8.5, while the conductivity rises by an order of magnitude independent of filler loading. The membrane linear swelling in water at 80 degrees C was also investigated and discussed on the basis of the filler hydration. (c) 2005 Elsevier B.V. All rights reserved.