Nafion membranes degrade in polymer electrolyte membrane fuel cells due to the interplay of physical and chemical degradation. In the interest of mitigating this problem, Nafion membranes were modified via an in situ sol-gel polymerization of titanium isopropoxide to generate titania quasi-networks. These composite materials are viewed as model systems within the context of durability without an immediate concern for cell performance. The modification did not influence membrane equivalent weight but reduced its hydration capacity. Membrane modulus increased, dimensional stability improved, creep lessened, and the ability of constrained membranes to withstand contractile stresses due to humidity change was greatly enhanced. The damage surface morphology of unmodified Nafion, viewed using scanning electron microscopy, and of constrained samples showed significant failure, whereas the modified membranes showed considerably more structural integrity. Open-circuit voltage (OCV) testing showed that the inorganically modified membrane held voltage better with fluoride emission at least an order of magnitude lower than that of the unmodified membrane. However, the performance curve of the modified membrane before the OCV test is inferior to that of Nafion; but after the test it is slightly better. This in situ sol-gel-derived inorganic modification offers a simple way to enhance membrane durability by reducing both physical and chemical degradation.