Open porous materials, with more than 90% air, are often included in multi-layer vehicle structures, like a car door or a train floor, to improve acoustic and thermal performance without adding much weight. Here the acoustic performance of open cell porous materials, with focus on flow resistivity, is modeled and evaluated based on simplified micro-structure models to investigate the effect of anisotropy. Two micro-geometries are analyzed and compared: the hexahedral model and the tetrakaidecahedron (Kelvin cell). The micro-models are elongated in one direction to study the influence of micro-structural anisotropy on the macro level flow resistivity. To evaluate how the redistribution of material effects on the flow resistivity, the porosity is kept constant. Both models can be used to predict average flow resistivity in the same range as measured materials. The flow resistivity components show large variations in different directions with increasing anisotropy, while the averaged flow resistivity is close to the isotropic value.