Fiber distribution in a polymer matrix composite plays a key role in moisture transport which in turn affects its long term behavior. In this paper, effect of filament arrangement on moisture diffusion is studied. The emphasis is on the effect of neighborhood filaments on a single filament placed in a polymer matrix. Fickian diffusion has been simulated using finite element method. Several microstructures have been created using variable angular and spatial orientations of the filaments. Their saturation times have been recorded and analyzed. Microstructures for most favorable saturation time have been identified. The results show that the diffusivity of composites can be controlled through careful spatial design of filaments. The observations should serve as a clue for designing optimum filament geometry for impeding moisture ingress and improving durability of composites. (C) 2014 Elsevier Ltd. All rights reserved.