Vibration isolation refers to procedures that prevent sound from transferring from one area to another. It aims to reduce or block acoustic emissions such as machine or traffic noise. Special vibration isolation materials like foams or elastomers (e.g., REGUFOAM FR) are used to reduce sound waves. Vibration isolation is especially important in areas where noise is disruptive, such as in residential buildings or trains.

The natural frequency is the inherent vibration frequency of a material or object. It plays an important role in vibration isolation because materials can be tuned to specific frequencies so as to better reduce vibrations and structure-borne sound. When a material like REGUFOAM FR is tuned to its natural frequency, it can effectively isolate vibrations, particularly in the affected frequency range. This means that disruptive noise is captured before it can spread through the structure.

Structure-borne vibration

Structure-borne vibration is a form of sound that spreads through solid materials such as walls, floors or metal structures. It occurs when vibrations, caused by mechanical impact—such as footsteps, machine operation, or the movement of trains—are transferred into a structure. These vibrations spread through the solid material and can be perceived as disturbing noise at other locations, often far from the source.

Structure-borne vibration decoupling

Structure-borne vibration decoupling is a method used to prevent or minimise the transmission of vibrations through solid structures. In this process, the direct contact between vibrating components (e.g., machine parts or tracks) and solid structures (such as walls or floors) is interrupted by special elastic materials like REGUFOAM FR. These materials act as buffers preventing the sound from spreading. This breaks the transmission of structure-borne vibration and significantly reduces noise, leading to greater comfort and less acoustic disturbances.

Structure-borne vibration is a form of sound that spreads through solid materials such as walls, floors or metal structures. It occurs when vibrations, caused by mechanical impact—such as footsteps, machine operation, or the movement of trains—are transferred into a structure. These vibrations spread through the solid material and can be perceived as disturbing noise at other locations, often far from the source. The density (i.e. volumetric mass density (VMD) or specific mass) describes the mass of a material per unit volume in kilograms. The adjustment capability of REGUFOAM FR allows the material to be optimally tuned for acoustic performance in different constructions.

EN 45545 & Hazard Level

EN 45545 is a European standard that defines fire safety requirements for materials and components used in railway vehicle construction. It specifies the properties a material must have to ensure the safety of passengers and staff in the event of a fire. The standard also specifies tests for flammability, smoke generation, toxicity and heat releases, categorising materials into different Hazard Levels (HL1, HL2 and HL3) depending on their location of use and the safety requirements in the train. The highest classification, HL3, requires a material to exhibit exceptionally robust fire protection properties and qualifies it for use in safety-critical areas.

Vibration isolation meets passive fire protection: Dual protection in one product

Keep noise out & safety in – vibration isolation and passive fire protection all in one

“We are not at the end of our markets yet,” begins Andreas Pfitzinger, Product Manager for Transportation at KuhnOdice. “Far from it!” adds Steffen Blecher, Sales Director of the Acoustics Division at REGUPOL. In this video podcast, the two discuss the background and successes of their collaboration.

At the centre of their conversation is REGUFOAM FR, an innovative material launched in the summer of 2024 that combines high-quality vibration isolation with reliable fire protection. Developed specifically for railway vehicles, REGUFOAM FR effectively reduces noise and vibration while meeting stringent fire safety requirements. Also, the material stands out for its flexible and tailored application.

Both Andreas Pfitzinger and Steffen Blecher agree that REGUFOAM FR is just the beginning. The partnership between KuhnOdice and REGUPOL opens up endless possibilities to make the future of transportation safer and more comfortable.

Video-Podcast REGUFOAM FR

#1: Why is comfort so important in the railway industry?

A quiet atmosphere is key for many travelers looking to relax or focus on work, especially on longer train rides. For more than 20 years, Regupol has been creating foam materials that effectively reduce noise in rail vehicles, helping to ensure a comfortable travel experience. Over time, the requirements for both sound and fire protection have grown. In response, REGUPOL has partnered with svt to develop materials that not only reduce noise and vibration but also meet the highest standards of fire safety.

#2: How does passive fire protection work with REGUFOAM FR ?

The polyurethane foam used for REGUFOAM FR is made flame-retardant by adding expandable graphite. When exposed to heat, the graphite expands and forms a non-combustible protective layer that acts as a safety shield, blocking heat and flames. This foamed graphite layer prevents the spread of fire.

#3: How does vibration isolation work with REGUFOAM FR?

For optimal vibration isolation, the sources of interference and frequencies are analysed to adjust the elastic mounting of REGUFOAM FR as required. The material has a specific natural frequency which, when properly set, effectively minimises sound transmission. REGUFOAM FR is industrially foamed and customised to meet client specifications, allowing flexible adaptation to acoustic and passive fire protection requirements.

#4: What standards & norms does REGUFOAM FR comply with?

In order to fulfil the high fire protection requirements in railway transportation, REGUFOAM FR must comply with standards such as EN 45545. The material is certified as compliant with the HL3 classification requirements – the highest level – allowing its use in all types of railway vehicles and train models. These comprehensive tests ensure that REGUFOAM FR is a safe and reliable material for railway applications.

#5: How does the combination of vibration isolation and passive fire protection look like in detail?

Using a model, we illustrate how structure-borne sound is transmitted through solid structures and how effective decoupling with elastic foams like REGUFOAM FR can reduce these vibrations. The foams are tuned to specific natural frequencies to isolate disruptive frequencies and minimise ambient noise. REGUFOAM FR provides a durable, combined solution for vibration isolation and passive fire protection thereby reducing service intervals and costs in rail vehicle manufacturing. In the future, the material can also be used in other industries, such as shipbuilding or aviation.

The floor makes the difference – how REGUFOAM FR provides quiet and safety

Cross-sectional representation of a train floor with built-in REGUFOAM® FR.

The above figure shows REGUFOAM FR installed as an elastic layer between the passenger compartment and the underfloor structure (e.g., made of wood, aluminium, steel or lightweight structures). This position effectively isolates structure-borne sound that would normally spread through solid structures, thereby reducing noise and vibrations in the passenger cabin.

Due to elastic decoupling and accurate tuning to specific natural frequencies, REGUFOAM FR selectively isolates frequency ranges that would otherwise cause unwanted noise. The material comes in four types REGUFOAM FR 221, 301, 401 and 511 with different densities designed to meet specific load requirements—from light to heavily loaded areas. To achieve optimal insulation it’s better to use softer elastomers for lightweight constructions. For heavier floor constructions, a harder type is required to prevent an overloading of the elastomer. This way, REGUFOAM FR can be adapted to different constructions.