A polymer electrolyte membrane (PEM) fuel cell stack requires gaskets in each cell to keep the reactant gases within their respective regions. Both sealing and electrochemical performance of the fuel cell depend on the long-term stability of the gasket materials. In this paper, the change in properties and structure of a silicone rubber gasket brought about by use in a fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140 degrees C) and greater acidity. The dilute sulfuric acid accelerated aging solutions used had pH values of 1, 2, and 4. In an additional test, Nafion (R) membrane suspended in water was used for accelerated aging, to more closely correspond to a PEM fuel cell environment. The analysis showed that acid hydrolysis was the most likely mechanism of degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. It was concluded that the accelerated aging test is a good one for rapidly screening materials for resistance to the acidic environment of the fuel cell. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013