Multi-layer insulation systems are widely used in many industrial sectors (particularly in automotive and aeronautic industries). They have a complex dynamic behavior due to the use of different materials like visco-elastic, poro-elastic and acoustic layers. The interface conditions between these materials play also a significant role in the global behavior. The paper concentrates on modeling poro-elastic layers using a 3-D finite element (FE) approach. A Biot model is selected for that purpose. A mixed displacement formulation is used. This can easily be coupled with other FE sub-models related to elastic thin shell layers or acoustic layers. Applications related to the prediction of the surface impedance of multi-layer configurations are presented.