Abstract : Over the past few years, car manufacturers have improved their numerical models for the prediction of the trimmed body vibroacoustic response. In the lowfrequency band [20,200] Hz, sound-insulation layer modeling remains a critical topic. Recent work allows the connection of the structure and cavity through a transfer matrix computed from a FE model of the soundinsulation layer. Nevertheless, such an approach requires a FE model of sound-insulation layer, which may not be available in early design stages. Moreover, considering the uncertainty of the design itself, in addition to material uncertainty, a deterministic model may not be appropriate. In this paper, a simplified model of sound-insulation layers based on the fuzzy structure theory is proposed. The way how the fuzzy model's parameters are related to design parameters will then be discussed. Finally, the application to a full trimmed body is presented.