The effects of the anisotropic bending stiffness of gas diffusion layers (GDLs) on the performance of polymer electrolyte membrane fuel cells with metallic bipolar plates (MBPs), having different channel depths, are investigated. The current-voltage performance of fuel cells with 90 degrees GDLs, whose directions of higher stiffness are perpendicular to the direction of the major flow field, is generally higher than that of cells with 0 degrees GDLs, whose directions of higher stiffness are parallel to the direction of the major flow field. In the shallowest channel, the air pressure drop (Delta P) values of the 90 degrees GDL cells are clearly lower than those of the 0 degrees GDL cells, indicating less intrusion of the 90 degrees GDL into the MBP channels. However, no significant difference appears between the air Delta P values of 0 degrees and 90 degrees GDL cells employing deeper channels. In comparison with other cells employing deeper channels, a dramatic increase in the high-frequency resistance of both the 0 degrees and 90 degrees GDL cells with the shallowest channel is unexpectedly observed, presumably due to the exceptional increase in the hydrogen and air pressure, which may cause more deformation and poor contact status of the GDLs in the cell. The cross-sectional images of GDLs upon compression indicate that the difference of blocked channel area between 0 degrees and 90 degrees GDL cells is much larger in the case of the shallowest channel, resulting in the observed air Delta P, whereas it is substantially negligible for the deepest channel. (C) 2014 Elsevier Ltd. All rights reserved.