This work aims at developing a 4-in-1 device to simultaneously measure parameters under compression (UC), including thickness (TUC), resistivity (RUC, through-plane), and in-plane permeability (IPP-UC), and to separately measure through-plane permeability (TPP). The simultaneous measurement of TUC/RUC/IPP-UC is accomplished through an annulus sample by measuring the flow rate–pressure relationship in a radial flow [1]. By adding a two-piece adaptor, TPP can also be measured using a disk sample. Typical TUC/RUC/IPP-UC/TPP curves of a gas diffusion layer (GDL) are shown in Figure 1. Upon the design requirements, the TUC/RUC/IPP-UC/TPP tester is calibrated and validated.The 4-in-1 device was originally designed for the characterization of the GDL, a key component of the membrane electrode assembly (MEA) for a proton exchange membrane (PEM) fuel cell. The GDL properties are greatly associated with the cell performance, especially under compression. To ensure the quality of GDLs, it is of great importance to characterize GDL properties with respect to the component standardization and specification. The application of the 4-in-1 device was later extended for the characterization of the porous transport layer (PTL), a crucial component for the anode of PEM water electrolyzer in responding to the increased research and efforts made in the development of, mostly, Ti-based PTLs for PEM water electrolysis [2]-[4] , as commercially available PTLs are basically materials borrowed from other applications, e.g., filtration.The developed TUC/RUC/IPP-UC/TPP device has been proven to be a useful tool for the quality control (QC) of GDLs and PTLs, facilitating the component development, complementing the component supply chain, contributing to cell reliability, and thus reduction of cost, for both the PEM fuel cell and PEM water electrolysis technologies. Acknowledgements This work is financially supported by the Office of Energy Research and Development (OERD) and the Advanced Clean Energy (ACE) Program of the National Research Council Canada (project #NRC-23-140).