It is shown here that properly designed fibrous media (e.g., glass or polymeric fibers) can be used to damp structural vibration as well as to absorb sound. The materials can then be multi-functional, reducing the number of elements required to achieve a specified level of noise and vibration performance. Past work demonstrated that layers of fibrous media placed on panels can damp the panel motion by removing energy from the nearfield acoustical motion generated by the panel vibration. The current study focused on designing the fibrous medium to ensure optimal vibration damping in a particular application. First, a method of calculating the response of a panel with an attached fibrous layer is recalled and updated to allow layers of limp or elastic porous media to be modeled. Example results will be presented, and then it will be shown that an optimal flow resistivity exists for a given frequency range and configuration of interest. Finally, based on a recently developed theory for the flow resistivity of fibrous media, the optimal flow resistivity identified in that way can be translated into a particular fiber size, given properties such as density of the fiber material and the desired superficial density
