A sound insulating trim part with acoustic mass-spring characteristics is provided. The sound insulating trim part includes a mass layer and a decoupling layer. The mass layer includes a porous fibrous layer with a dynamic Young's modulus E of at least about 96·AW·t (Pa), with AW being an area weight (g/m2), and t being a thickness (mm) of the porous fibrous layer. The mass layer also includes an air impervious thin barrier layer. The barrier layer is disposed between the porous fibrous layer and the decoupling layer. The barrier layer, the porous fibrous layer, and the decoupling layers are laminated together.