The addition of metal oxide particles to recast Nafion membranes improves fuel cell performance, particularly at high temperatures and reduced humidity. Operation under these conditions is desirable for enhanced CO tolerance and heat management, yet often causes membrane drying, reducing proton conductivity and over-all cell performance. Membrane mechanical and water-sorption properties were examined and comparisons were made between Nafion and Nafion/Titania composite membranes. Nafion/Titania composite membranes hade a slightly higher swelling pressure, consistent with a slightly higher Young's modulus. The interplay of thermodynamics and kinetics in Nafion water sorption-sulfonic acid solvation, concentration-driven and concentration-dependent diffusion, etc. were examined in light of measured mechanical properties of the membrane. This is an abstract of a paper presented at the 2006 AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).