The mechanical properties of gas diffusion layers (GDLs) in proton exchange membrane fuel cells (PEMFCs critically govern compression-dependent transport phenomena that control local performance and durability. This work presents a systematic, self-consistent characterization of orthotropic mechanical behavior, through-plane (TP) thermal and electrical conductivities, in-plane (IP) gas permeability, and structural properties for five commercial GDLs—wet-laid carbon papers (Toray TGP-H-060 with 5 and 30 wt% PTFE; SGL 29BA uncoated; SGL 28BC MPL-coated) and one hydroentangled non-woven (Freudenberg H23C7)—measured under controlled compressive loads (0.5–3 MPa). Additional GDL materials are benchmarked against literature data. Increased PTFE content significantly stiffens the fibrous network, while microporous layer (MPL) addition introduces additional through-plane bulk transport resistance. In-plane gas permeability decreases by approximately 70–90% over the investigated compression range for all materials, with the most pronounced reductions (up to two orders of magnitude) observed in SGL 28BC due to pronounced MPL intrusion into the substrate, forming a mixed fiber–MPL zone that reduces lateral macropore connectivity and increases flow resistance. Physically motivated models are applied to interpret the observed trends. Effective percolation theory correlations describe the nonlinear evolution of thermal and electrical conductivities with solid volume fraction, yielding interpretable parameters that explain material class differences and thermal − electrical decoupling. In addition, a hyperelastic two − power-law strain energy framework that mechanistically captures the full compressive response − from initial fiber bending, through topology-controlled stiffening, to high-strain densification − while maintaining thermodynamic consistency and finite-element compatibility is proposed. While Toray TGP-H-060 is extensively benchmarked in the literature, coupled compression-dependent multi-property datasets remain scarce for hydroentangled non-woven GDLs and MPL-coated roll-good grades. The comprehensive dataset and modeling framework presented here provide a robust foundation for high-fidelity three-dimensional PEMFC stack simulations, enabling improved material selection, stack design, and performance and durability optimization.