When geometric parameters, such as volume and thickness, are constraints to be considered in real applications and an increase of performance is required, other parameters must be taken into account for the optimization of fuel cells. The physical properties of bipolar plates, electrodes, and membranes are some of the parameters that can still be studied when maximum power output is sought under geometric constraint. This paper investigated the influence of porosity of the diffusive and reaction layers on the power output of an alkaline membrane fuel cell (AMFC). An experimentally validated mathematical model was used to simulate the fuel cell performance as a function of different porosities of the electrode. It was found that the change of porosity of the diffusive layer has a minimum influence in the power output of the fuel cell when the porosity of the reaction layer is kept constant. The cathode was shown to limit the performance of the fuel cell due to losses that make the polarization curve to drop to zero at the cathode faster than at the anode. The increase of the porosity of the reaction layer is verified to be an alternative to enhance the power output of the fuel cell.