Carbon nanofibers (CNFs) are grown on graphite fiber felt with a desired shape and dimension to form a structured carbon nanofiber composite. This CNF composite has a bimodal porous structure, containing macropores due to the intertexture of graphite fibers and mesopores due to the intertwist of CNFs. The pressure drop of the composite is derived from the convective flow of fluid through the macropores and is independent of the mesopores. Both viscous and turbulent resistance increases with the CNF's loading. After being wetted with cyclohexane and dried in the air, the CNF's layer shrinks and becomes smoother, and the composite has a much smaller viscous and turbulent resistance for the fluid. An extended Ergun equation is developed and is shown to be able to predict very well the pressure drop from the structural parameters that are related to the CNF's loading, i.e., macropore porosity and expanded diameter of the graphite fibers.