The change in mechanical properties of a catalyst coated membrane (CCM) as a function of humidity and temperature is investigated and compared to that of a pure perfluorosulfonic acid (PFSA) membrane at the same conditions. The results of tensile tests indicate that the modulus and yield stress of the CCM vary differently than those of the membrane with respect to temperature and humidity. Both materials decrease in stiffness and strength at higher temperature and humidity, but proportionally more so for the CCM leading to less desirable mechanical properties at typical fuel cell operating conditions. Length-wise swelling of the two materials during hydration is also investigated and is shown to be almost twice as great for the pure membrane material versus the CCM. The tensile forces induced by dehydration of constrained samples are also measured. The peak and residual dehydration forces are larger for the CCM compared to the membrane by a factor which occasionally exceeds the average reinforcement provided by the catalyst layers. These results emphasize the importance of the catalyst layers on the overall mechanical properties of the CCM and the need to consider them when attempting to model in situ stress distributions. (c) 2013 Elsevier B.V. All rights reserved.