Our insulations leave the noise outside

Spring mass systems consist of two layers, which are in direct contact with the sheet metal of the car body. 

A high-mass layer made of low-expansion foam or film lies on top of a springy layer, e.g. of soft foam or fibre fleece. Due to this decoupling of the mass layer from the sheet metal of the car body, the acoustic effect of the mass is considerably increased, as its physical inertia can be optimally adjusted to the inbound oscillation amplitude because of the springy support.

To achieve a comparable insulation effect exclusively with low-expansion foam or film a charge weight many times higher would be required. Thus the spring mass configuration constitutes a contribution to weight reduction by means of optimum use of heavy masses.