Since 2014 several collaborations between two laboratories of INSA Lyon - Mateis (materials science) and LVA (vibroacoustics) - have been focused on the modeling, designing and measuring hybrid sandwich composites structures with optimized damping properties for given frequency domains. The proposed contribution gives an overview of these modeling and experimental efforts, by presenting some results on several application cases. In a first study ([1-4]), a three layer steel/polymer/steel plate sandwich system is considered. Several aspects are studied by comparing four measurement techniques and three analytical models predictions. High resolution modal analysis coupled to contactless measurement of the velocity field of plates (CFAT) leads to the estimation of the equivalent single layer complex rigidity (frequency dependent “apparent bending stiffness” and “apparent damping”) for the whole [40Hz-20kHz] frequency band. Compared to the analytical modelling of Guyader based on wave propagation analysis, the results are in very good agreement. The comparison with this theoretical approach allows identifying the frequency dependent complex modulus of the polymer core layer through inverse resolution. The predicted properties turned out to match DMA measurements performed on the polymer material alone and the associated high frequency predictions (using the time-temperature equivalence principle). With this approach, the design of multilayer plates for vibroacoustics applications with optimized damping properties for given frequency domains may be performed. The second study ([5,6]) focuses on controlling the spatial in-plane viscoelastic properties of the polymeric core of sandwich structures. Aiming at creating materials by design, the tuning of the in-plane local material properties is pursued. The spatial patterning is achieved using a recently developed UV irradiation selective technique of Room Temperature Vulcanization silicone elastomeric membrane. “Structured” three-layer beams (aluminum/silicon/aluminum) with different core patterns (homogeneous and heterogeneous) are designed and tested. Fair model-experiments comparisons are obtained. This work permits the enunciation of guidelines for designing complex architectured systems with further control of the vibro-acoustics performances. In particular the effect of the viscoelastic patterning on the “optimum shearing zone” (position and width) will be discussed. The explored material solutions could be dedicated from low to very low frequency ranges where meta-material-based solutions are often inefficient. 1.Ege et al., Inter-Noise 2015, San Francisco 2.Roozen et al., JSV 2017, 390, pp.257-271. 3.Roozen et al., JSV 2017, 395, pp.90-101. 4.Ege et al., JSV 2018, 426, pp.129-149. 5.Gallo et al., Acoustics'2017, Boston. 6.Gallo et al., ISNVH 2018, Graz.