Where the diagonal elements define the orientation strength for the corresponding directions. After the generation of carbon fibers, the binder (PTFE) was then incorporated into the GDL domain with the desired solid volume percentage. The Geometric Tortuosity (𝜏) was then computed to characterize the GDL microstructure. The calculation of geometric tortuosity was conducted in the direction perpendicular to the direction of the carbon fibers using the following equation: