We use the Cuda-based Hybrid Approach for Octree Simulations (CHAOS) DSMC solver to predict gas transport coefficients of Morgan felt and FiberForm TPS materials with sample size of (1 x 1 x 1) mm(3). The detailed velocity flow-field of the pressure-driven flow through these materials is studied to compare the effect of material microstructures on gas transport. It is found that the effective flow path traversed by the gas is more circuitous and longer for FiberForm compared to the more porous felt. The obstruction offered by the material and the circuitous flow path is quantified by the Klinkenberg-derived permeability and hydraulic tortuosity factor, which are key material properties that govern the momentum transport through porous media. We also compute the hydraulic pore diameter of these materials and find that the through-thickness and in-plane pore diameter is equal to 86.94 and 98.7 mu m for felt and 36.25 and 60.9 mu m for Fiberform, which is within 5-6% of the average pore-size obtained from the tomography images. (C) 2018 Elsevier Ltd. All rights reserved.