Research and specialization are key processes in the development of effective, safe products that meet market needs. After over 80 years developing solutions and working side by side with our customers and suppliers, Concentrol has become one of the benchmarks in the chemical sector worldwide.

At the Perfomance Materials division, Concentrol manufactures solutions for the automotive sector, such as mold release agents for polyurethane foams, stabilizers or silicone surfactants for polyurethane foams and mold cleaners, among others.

Next we will see the most used materials and the manufacturing process for acoustic insulation for the automotive industry, also called ‘soundproofing’, or ‘soundproofing systems’. In addition, there will be a brief explanation on the release agents, an essential product for the manufacture of these parts, and the rest of the solutions for this sector.

The main materials used to make acoustic insulation for the automotive industry are composite materials and polyurethane.

Regarding polyurethane, the parts are made entirely from only polyurethane foam, or combined with other materials such as rubber, phenolic and polyspan, among others. The most widely used type of PU foam is high resilience (HR) flexible foam, but we can also find densified flexible foam, viscoelastic and R.I.M process. 

Insulation is achieved thanks to “acoustic barriers”, which are molded parts used in the automotive sector basically with the purpose of acoustically insulating the passenger compartment as much as possible.

PU foam exhibits excellent behaviour because noise enters through the pores and dissipates inside the foam. The ability to regulate the pore allows absorbing noise in a precise and measurable way.

These parts, or soundproofing systems, are incorporated into the vehicle interior, the boot and the engine. The most common is to find them under the dashboard, on the entire surface between the engine and the passenger compartment, to avoid the noise that the engine produces when operating. On the floors and the boot they are also strategically present, avoiding the transmission of noise to the passenger compartment.

Acoustic insulation with polyurethane


Types of materials

There are different types of materials that can be used as soundproofing. Composite materials such as phenolic resins and rubber agglomerates, as well as polyspan inserts, non-woven or other materials within molded polyurethane (PU) parts, among others.



Composite materials

Because of its quality and performance, PU is the most suitable, and that is why in many cases we come across a part totally made of injected polyurethane on an EPDM blanket, carpet or R.I.M. polyurethane.

Another type of cold curing foam that we can find on the market is the “densified flexible”. As its name indicates, it is flexible foam with a higher density, so that it is clearly harder, with a smaller internal pore and almost closed on the surface. Small filler and / or acoustic protection parts are typically manufactured in the automotive industry. Some examples are: padding in the gear shifter area, padding in the clutch and accelerator pedal areas, specific bodywork soundproofing, etc.

Due to its higher density, the part tends to swell inside the mold, and at the time of demolding it can pose problems if the release agent does not provide extra slip. Greasy water-based mold release agents are usually used, despite the fact that they are usually used at low temperatures and in quite deep molds, since they meet the lubrication requirement of the parts, facilitating their extraction. Unlike large parts, the small ones do not have any type of material other than the densified flexible one. 


Manufacturing process

For the manufacturing process we focus on the PU that interests us. It is always done through a cold molding process, and for them there are two distinctions:

  • Full PU part

It is the typical process of molding, application of the release agent, injection of the components in the mold and after curing, extraction of the part.

  1. Mixed part

Normally a rubber sheet is deposited in the mold (it is usual to preheat it first to increase its surface adhesion) and the PU is injected on top. When removing the part, one side is made of rubber (barrier) and the other made of PU (adsorption). This “barrier” part can also be made of other materials besides rubber, such as PU R.I.M. In this case, the R.I.M. sheet is previously molded and then it is deposited in another mold, where the flexible PU is injected on top.

As we have mentioned before, inserts can be used in the PU parts to improve their properties or facilitate assembly inside the vehicle. 



The fundamental thing is to obtain the acoustic function. It is considered that the ideal thing is that the area where the part receives noise is absorbent, and the end face, which is in contact with the passenger compartment, is a barrier. It is not totally clear however, so sometimes it is like that and sometimes the other way around, always having to work according to the indications of the clients.

Concentrol solutions

Concentrol offers a wide range of solvent-based (class I, II, III), water-based, co-solvent and hybrid release agents for this application. In addition, we have an extensive range of silicone surfactants, specifically designed for flexible HR polyurethane foam, and other auxiliary products such as reinforcing pastes, contact glues, mold cleaners, among others.

Release agents for polyurethane:

All mold release agents for the cold curing process are suitable:

  • Solvent release agents (class I, II, III according to flash point).
  • Co-solvent water-based (5 – 20% water) and water-based (<5% solvent) release agents.
  • Hybrid release agents (50 – 70% water).

Concentrol’s know-how consists of, once the problems and specific requirements of polyurethane soundproofing manufacturers have been detected, finding the best solution, which involves designing the most suitable skin for each need.

Other specialities of ours at Concentrol are silicone surfactants for all those manufacturers of these acoustic systems that are self-formulating. We also have complementary products such as reinforcement pastes (solvent-based or water-based), contact adhesives (for repairing foams), among others.

At Concentrol we are specialists and a global reference in solutions adapted to the client from custom manufacturing to the support we provide to industries in their different processes. In addition, at the Performance Materials division we have developed an extensive catalogue of solutions for the automotive sector.

 Authors: Jordi Fornells, Rafael Fernández, Ángel Rodríguez y Nikoleta Raykova.