Abstract: A kit for reducing noise in motor vehicles having at least one areal vehicle part, the kit having a sound-insulating assembly package having several layers and an at least partly interlaying air layer. This assembly package has at least one porous cushioning layer, a microporous reinforcing layer which is lightweight, stiff and openly porous, an air flow resistance between R.sub.t =500 Nsm.sup.-3 and R.sub.t =2,500 Nsm.sup.-3, and a surface area of mF=0.3 kg/m.sup.2 to mF=2.0 kg/m.sup.2. The reinforcing layer has a stiffness of B=0.05 Nm to B=10.5 Nm. This permits replacing the weight of classic spring-mass-systems for noise reduction in vehicles with a system at least 50% lighter. In addition to the dampening effect on oscillations, this kit absorbs sound and provides thermal insulation. Preferably, this multifunctional, ultralight kit is used to insulate the floor or firewall, or as a door lining or roof inner lining.