In the framework of the Silent Wall ANR project, the CMM and the US2B are associated in order to characterize and to model fibrous media studying 3D images acquired with an X-Ray microtomograph used by the US2B. The device can make 3D images of maximal size 23043 voxels with resolutions in the range of 2–15 µm. Using mathematical morphology, measurements on the 3D X-Ray CT images are performed to characterize materials. For example, measuring the covariance on these images of an acoustic insulating material made of wooden fibers highlights the transverse isotropy of the fibers orientations in the xOy planes perpendicular to the compression Oz axis. Moreover, it is possible to extract other morphological properties, such as the size distribution either of the fibers or of the pores by estimating the morphological opening granulometry of the considered medium. Finally the morphological tortuosity of the fibrous and porous networks are estimated from geodesic propagations. The tortuosity is a parameter which can help to link physical, acoustic, and morphological properties of the material. Moreover the effects of the boundary layer, where viscous and thermal damping of the sound take place, are studied from the point of view of the tortuosity.