<p>Proton exchange membrane fuel cell (PEMFC) is a promising clean energy source, but its performance and stability are vulnerable to the negative effects of humidity conditions. The gas diffusion substrate (GDS) plays a pivotal role in regulating the moisture and gas transport. The single pore structure of traditionally designed GDS often leads to the pathway competition between moisture and gas, which effects the efficiency of fuel cells. In this study, we report on a hierarchical fibrous paper with tunable hierarchical pores for a sustainable GDS. This design offers gas permeability under wet conditions, by separating the gas pathway from the moisture pathway, thus mitigating their pathway competition. In addition, this paper forms a multi-scale scaffold that absorbs moisture under high humidity conditions and releases it under dry conditions. It is allowed to maintain an optimal internal humidity and further enhances the humidity adaptability. Furthermore, the carbon footprint is only 15.97%, significantly lower than commercial alternatives. This feature makes it a sustainable solution to stabilize PEMFCs under diverse humidity conditions. </p> Graphical abstract <p></p>