Microstructure-property relationships in a gas diffusion layer (GDL) for polymer electrolyte fuel cells, part I : effect of compression and anisotropy of dry GDL

•Methods are developed to predict transport properties of dry GDL in PE Fuel Cells.•Diffusivity and Permeability are reliably predicted based on 3D characteristics.•Predictions based on 3D microstructure match well with numerical simulations.•Anisotropy is due to in- and through-plane variation of tortuosity and hydraulic rad.•The methods can be used to predict relative permeability and diffusivity in wet GDL.