Particle image velocimetry was used to measure 2D velocity fields in representative regions of interest within flow channels of interdigitated and single-serpentine proton exchange membrane (PEM) fuel cell models. The model dimensions, gas diffusion layer (GDL) permeability, working fluid, and flow rates were selected to be geometrically and dynamically similar to the cathode-side airflow in a typical PEM fuel cell. The model was easily reconfigurable between parallel, single-serpentine, and interdigitated flow fields, and was constructed from transparent materials to enable optical imaging. Velocity maps were obtained of both the primary and secondary flow within the channels. Measurements of the secondary flows in interdigitated and single-serpentine flow fields indicate that significant portions of the flow travel between adjacent channels through the porous medium. Such convective bypass can enhance fuel cell performance by supplying fresh reactant to the lands regions and also by driving out product water from under the lands to the flow channels.