Abstract: The invention relates to a proton exchange membrane fuel cell and a method of designing the same. A method of designing a proton exchange membrane fuel cell comprising a gas diffusion layer is described. The method comprises: using a model of the proton exchange membrane fuel cell to determine performance of the fuel cell, wherein the model is based on a plurality of parameters of the fuel cell, the plurality of parameters including at least one anisotropic property of the gas diffusion layer, adjusting at least one of the plurality of parameters; determining whether or not performance of the fuel cell is improved by the adjusting step and designing the fuel cell by selecting the parameters which provide improved performance. A proton exchange membrane fuel cell is also described comprising a gas diffusion layer, the proton exchange membrane fuel cell having a plurality of parameters, wherein the parameters are selected to provide substantially uniform temperature distribution across the gas diffusion layer.