Damping Materials - Rubber and PU Rubber

Effective damping of mechanical oscillations, shocks and vibrations is a central criterion in the design of technical systems. Materials such as rubber and polyurethane rubber (PU) are characterized by high damping power, viscoelastic behavior and adjustable mechanical characteristics. Their targeted selection and modification allow for application-specific adaptation to dynamic loads, environmental conditions and service life requirements. We highlight the typical material properties, use cases and current developments in the area of damping polymer materials.

Rubber, Polyurethane and PU Rubber (PUR)

Rubber is the classic term for rubbery materials. This includes both natural rubber and various synthetically produced elastomers such as NBR or EPDM. Typical for rubber: high elasticity, good vibration damping and a soft, rubbery character. It is particularly suitable for components where mobility and vibration insulation are required - such as machine feet, rubber buffers, flexible bearings or also in combination with gas struts for shock reduction.

Polyurethane (PU), on the other hand, is a synthetic plastic - an extremely versatile one. PU can be hard like a plastic housing or elastic like a rubber - depending on the chemical composition. In industrial practice, the elastic variant is often used for damping applications, which is particularly abrasion-resistant, has high tensile strength and is chemical-resistant.

So-called elastic polyurethane, or PU rubber, is rubber-like soft and elastic, but is mechanically more robust than conventional rubber. It combines the damping properties of an elastomer with the wear resistance of a technical plastic.

In addition to rubber and PU rubber, which are characterized by a viscoelastic behavior, there are special plastics that are characterized by special properties such as high temperature resistance, chemical resistance and mechanical strength. To learn more, check out our blog about properties, resistance, and application examples of special plastics.

Properties and Applications of Rubber and PU Rubber

Materials with damping properties play an important role in numerous industrial applications - from mechanical engineering and material handling to plant insulation. Wherever vibrations, shocks or recurring loads occur, materials that are not only elastic but also durable, dimensionally stable and adaptable to environmental conditions must be used. Damping materials must be able to absorb mechanical energy in a controlled manner and convert it into heat. Rubber and PU rubber have special physical and mechanical properties that make them ideal. What these are and how they can be used specifically for various industrial applications is explained below. You can find even more concrete practical examples in our supplementary blog on damping materials.

Elasticity and resilience

A central property of damping materials is their ability to elastically deform. Both rubber and PU rubber are characterized by a high degree of elasticity and recovery capacity. This makes them ideal materials for shock absorption and vibration isolation in mechanical engineering, plant construction and material handling.

Rubber is particularly elastic: It can be greatly stretched and returns to its original shape after the load is removed, without permanent deformation. This property is critical for components such as vibration elements, machine bearings or damping inserts.

Depending on its design and hardness, PU rubber also offers very good elasticity - but with a higher resistance to returning to its original shape. This means that the material “brakes” more when deformed and can thus dissipate additional energy. This behavior is particularly advantageous in applications with recurring shock or compressive loads.

Both materials protect sensitive machine elements from overload, reduce vibration and extend the life of technical systems. Thanks to their elastic properties, they are ideal for damping components in industrial applications.

Viscoelastic behavior

Another feature of rubber and PU rubber is their so-called viscoelastic behavior. It describes the ability of a material to handle mechanical stress both elastically (immediately reversible) and viscously (delayed and damping). This combination ensures that during dynamic loading, such as due to vibrations, shocks or impulsive forces, a portion of the motion energy is not simply suddenly returned, but converted into heat as deformation energy and thus permanently dissipated. This is exactly what makes rubber and PU rubber so effective in vibration isolation and shock absorption.

While rubber is naturally viscoelastic, the behavior of PU rubber can be specifically adjusted via the formulation. In practice, this leads to significantly reduced vibrations, better noise performance and higher protection of machine components. Typical applications include vibration elements, damping bearings, elastomer parts for conveyor systems or machine feet.

High damping power (loss factor)

A key characteristic in the selection of damping materials is the so-called loss factor, also known as the loss factor. It describes the relationship between elastically stored energy and energy dissipated as heat within the body in a viscoelastic material. The higher this value, the more mechanical energy is converted to heat rather than returning as rebound or vibration.

Rubber naturally has a relatively high loss factor, making it a particularly effective material for shock and vibration damping. At the same time, however, this effect also leads to increased heat generation under dynamic loading, which must be taken into account depending on the application. PU rubber, on the other hand, can be formulated specifically with medium to high damping power. Depending on the composition, PU rubber may be designed to either damp more or store more energy.

High loss factor materials are preferred for shock absorbers, buffer and insulation elements where maximum energy absorption is essential. For dynamic bearing elements or spring-loaded designs where some restoring force is desired, materials with a lower damping factor are preferred.

Adjustable Hardness (Shore Hardness)

The hardness of a material is a key characteristic when selecting damping components. In the international context, it is usually measured according to the Shore hardness standardized with a uniform measuring setup for rubber and polyurethane rubber, in particular Shore A for softer elastomers and Shore D for harder plastics. In addition, the Asker hardness standard is particularly common in Asia, which uses a similar test method but its own scales, e.g. Asker C, Asker F or Asker A. In practice, both systems serve to evaluate the resistance of a material to the penetration of a standardized test specimen. Both characteristics can be correlated over wide ranges. For example, a Shore A 50 corresponds to approximately Asker C 70. The differences lie in the details: Asker measures slightly more sensitively in the softer range, which may be beneficial in certain applications. You can find more about test methods in our blog on hardness grades and hardness testing.

Rubber typically ranges from Shore A 30 to Shore A 80. It can thus be adjusted from very soft to medium-hard and is therefore very well suited as a vibration damper for machines, machine bearings or elastic inserts with high deformability. PU rubber offers a significantly wider hardness spread: from Shore A 30 (soft to medium-hard plastics) to over Shore D 80 (medium-hard to very hard plastics). As a result, PU elastomers can be designed to be both rubber-like soft and very stiff and rigid, depending on the requirements in the component.

In industrial applications, this means: Soft PU rubbers are ideal for shock-absorbing buffers, vibration elements or mountings. Harder versions are ideal for highly loaded rollers, guides, or impact protection elements where dimensional stability and abrasion resistance are the primary considerations.

Tear elongation and abrasion resistance

Damping materials must not only be elastic, but also be able to withstand sustained mechanical stresses, especially in applications with heavy movement, friction or localized stresses.

Rubber naturally offers a very high tear elongation and thus excellent properties for dynamic applications. Abrasion resistance is also good in many rubber types, making it a proven material for bearing, damping, and spring elements. PU rubber goes one step further: Its abrasion resistance is up to five times that of conventional rubber, while maintaining high tear and notch resistance. This makes PU rubber particularly suitable for wear-intensive applications in which continuous mechanical loading must be combined with elasticity. In practice, this ensures a significantly longer service life under vibration, friction or impact loads.

Chemical and temperature resistance

In many industrial environments, elasticity alone is not enough. Chemicals, oils, humidity and temperature fluctuations place additional requirements on the material. This shows significant differences between rubber types and PU rubber.

Rubber offers specific chemical resistances depending on the type: Thus, NBR (nitrile rubber) is very resistant to oils and greases, while EPDM is particularly resistant to weather and ozone. The typical temperature range is between -40 °C and +100 °C, in special blends also above. PU rubber offers broad chemical resistance, especially to oils, greases, coolants and solvents. Ether-based polyurethane rubber is particularly resistant and is not prone to hydrolysis. On the temperature side, PU rubber also offers advantages and can be used continuously up to +120 °C depending on the formulation.

In practice, this means that PU rubber is ideal for use in lubricant-exposed machinery areas, in conveying systems with cleaning or chemical exposure, and in environments with varying temperature conditions. Rubber, on the other hand, remains the right choice when specific media must be reacted to – such as outdoors or when exposed to specific oils.

Factors influencing the choice between rubber and PU rubber

Both rubber and elastic polyurethane (PU rubber) are proven damping materials, but they differ significantly in their properties. Depending on the use case, one or the other can offer clear advantages.

Selection by type of load

An important factor is the type of mechanical loading. If a component is primarily intended to absorb vibrations or continuous oscillations, rubber is usually the better choice as a vibration damper and oscillation damper. Its pronounced elasticity and high damping power make it ideal for applications such as machine mountings, vibration elements, or decouplings. PU rubber, on the other hand, shows its strengths especially under shock-like or impulsive loads. Due to its higher rebound resistance, it can absorb and dissipate kinetic energy in a targeted manner, which makes it particularly suitable for impact protection strips, rubber buffers, or elastic stops.

Selection according to hardness requirement

The hardness requirement also influences the material selection. While rubber is typically in the range of Shore A 30 to 80, PU rubber offers a much wider range. Depending on the formula, it can be set to be both rubbery soft and almost hard plastic – from Shore A 30 to Shore D 80 and above. This allows PU rubber to be adapted very flexibly to the requirements of different designs, such as rollers, damping modules or bearing elements with defined deformation behavior.

Selection based on environmental conditions

Another central aspect is the environmental conditions. PU rubber is inherently highly resistant to oils, greases, coolants and chemicals. It also shows high stability under UV radiation and weathering. Rubber also offers good resistance, but depending on the type selected. For example, NBR is highly oil resistant, while EPDM is ideal for outdoor applications. For applications in harsh industrial environments where components regularly come into contact with media or changing temperatures, PU rubber often offers the more robust solution.

Selection taking into account continuous load

When it comes to dynamic continuous loading, another advantage of PU rubber becomes apparent. It features high dimensional stability, low permanent deformation, and excellent fatigue strength. This makes it particularly durable in moving or impact-bearing applications such as conveyor rollers, guide elements or elastic couplings. Rubber, on the other hand, tends to suffer from material fatigue under continuous loading and at high temperatures, which can limit the service life.

Selection based on cost and benefit

Economic considerations also play a role in selection. Rubber is usually cheaper to manufacture and is well suited for standard applications with moderate loads. PU rubber is usually more expensive, but offers a much longer life under demanding conditions. For highly loaded components with mechanical wear or chemical effects, the use of PU rubber can therefore be economically rewarding in the long term despite higher initial costs.

Current developments and innovations

Damping materials such as rubber and PU rubber have been an integral part of mechanical engineering, material handling and industrial design for decades. However, the materials, manufacturing processes and application concepts continue to evolve in this established area. New technologies and increasing requirements - for example in terms of durability, sustainability or multifunctionality - are driving material development decisively.

Hybrid materials and composites

A clear trend lies in the development of cross-material solutions in which rubber, in particular synthetic rubber, or PU are specifically combined with other materials - such as metals, thermoplastics, textile structures or technical fibers. These composites allow mechanical damping to be combined with structural stability, thermal conductivity, or functional surfaces. In particular, the combination with reinforcing fibers allows components to be developed that have improved tensile strength, tear strength and dimensional stability despite high flexibility. This allows elastomeric components to be produced that remain permanently stable even under tensile or bending stress without losing their damping properties.

Additive manufacturing (3D printing) of PU elastomers

Additive manufacturing (3D printing) of elastic polyurethanes is another area of innovation with growing industrial importance. New 3D printing processes enable the processing of highly flexible PU materials with defined damping behavior, directly from digital CAD data. This opens up new possibilities in prototype development, small series production or component customization - e.g. for customized rubber buffers, dampers or structural parts with integrated functional zones. Geometrically complex structures such as grids, cavities or stepped hardness curves can also be realized in this manner.

Sustainable formulations and recyclability

With increasing environmental requirements, the sustainability of damping materials is also becoming more of a focus. New formulations rely on bio-based polyols, recycled raw materials or solvent-free processing methods. In the field of polyurethane, a versatile special plastic, intensive work is being performed on thermoplastically processable elastomers (TPU) that are easier to recycle. Rubber materials are also progressing towards green vulcanization, the use of renewable fillers or the mechanical recovery of used rubber parts. This makes it increasingly possible to produce long-lasting damping components with a reduced environmental footprint.

Functional integration in material design

Another development concerns the integration of additional functions directly into the material or the component structure. As a result, damping materials are increasingly equipped with conductive, temperature-resistant or sensor-active properties. For example, PU rubber can be equipped with conductive additives to prevent electrostatic charging - relevant in conveyor technology or packaging solutions for electronics. Sensor integration for condition monitoring or wear detection directly in the damper element is also increasingly realized, for example by embedding strain gauges or RFID components.

Optimized formulations and performance tuning

In parallel, manufacturers are continuously working to optimize existing formulations, such as new plasticizers, fillers, crosslinkers, or additives. The goal is to provide even more precise control of damping, rebound behavior, thermal load capacity or media resistance. Today, modern PU systems can be produced, for example, with a highly adjustable loss factor - individually adapted to the dynamic load profile of an application. There has also been progress in the area of sound-damping properties through targeted microstructuring or the use of porous filling systems.