The effects of relative alignment of two different types of an-isotropic open cell porous materials are investigated in terms of the acoustic response of a multi-layered configuration. Numerical experi-ments, where gradient based optimization techniques were used, are con-ducted to find possible extremal values. It is shown that, depending on the degree of anisotropy of the porous material properties, their angular orientations have a significant and frequency dependent influence on the measured response. The results highlight the importance of further advancing the knowledge of anisotropic porous material behavior.