Shore hardness of polyurethane
Shore hardness determines how much a polyurethane component deforms under load and how it performs in operation. It influences factors such as damping, elasticity, rebound, wear resistance, and load-bearing capacity. This guide explains what shore hardness means, the difference between Shore A and Shore D, and which hardness ranges are suitable for rollers, wheels, buffers, dampers, and PUR molded parts. INTERNORM manufactures polyurethane components from 10 to 95 Shore A, offering one of the widest hardness ranges on the market.
What is Shore hardness?
Shore hardness is a standardized metric for measuring the indentation hardness of elastomers and plastics. It is measured using a durometer, which presses a standardized indenter into the material under defined pressure. The lower the penetration depth of the indenter, the higher the shore hardness and the harder the material.
Measurements are taken according to the DIN EN ISO 868 standard. This standard ensures that hardness values are determined consistently regardless of the manufacturer, allowing for reliable comparison in technical drawings, specifications, and international supply chains.
The shore scale ranges from 0 to 100. A value of 0 represents maximum penetration depth, indicating a very soft material. A value of 100 means the indenter barely penetrates, indicating a very hard material. According to the standard, the measurement is read after a test duration of three seconds. The method is named after the American engineer Albert F. Shore, who developed the first Shore durometer in 1915. Since then, Shore hardness has become the globally recognized standard for characterizing elastic materials.
For PUR components, shore hardness is the decisive selection criterion during design. It significantly determines how much a component deforms under load and what function it performs in use. Whether a polyurethane solution is intended to dampen, guide, press, seal, or transport—the right shore hardness is the foundation for performance, service life, and operational safety.
At INTERNORM, we manufacture polyurethane components in a hardness range from 10 to 95 shore A, covering an exceptionally broad spectrum of applications.
Shore A or Shore D:
Which scale applies to PUR components?
Two shore scales are generally used for polyurethane components: Shore A and Shore D. Which scale is used depends on the hardness of the material and its intended application.
Shore A is used for soft to medium-hard elastomers. This includes rubber, silicone, and most cast polyurethane materials. Typical components include rollers, wheels, buffers, seals, wipers, and technical molded parts. In this range, elasticity, damping, and deformability are precisely tailored to the specific application.
Shore D, on the other hand, is used for significantly harder materials. Typical examples include technical plastics such as PE-HD or PA6. For polyurethane, this scale only becomes relevant in very high hardness ranges and is used more frequently for hard TPU injection-molded parts than for classic PUR cast parts.
Practical note: Shore A and Shore D are two different hardness scales. The scales were developed for different types of materials and use different testing methods. Elastic materials such as cast polyurethane, rubber, or silicone are usually measured in Shore A, while hard plastics are predominantly evaluated according to Shore D.
Measurements are carried out in accordance with DIN EN ISO 868 or, internationally, ASTM D2240, ensuring that hardness values are comparable worldwide and clearly defined in technical specifications.
The correct Shore hardness by component category
Shore hardness is not an abstract value, but a decisive factor for the function of a PUR component. Softer materials offer a larger contact surface, better damping properties, and are gentler on sensitive surfaces. Harder materials deform less, allow for higher power transmission, and ensure more precise guidance. The appropriate shore hardness for a component therefore always depends on the specific requirements, loads, and operating conditions. The following overview shows typical hardness ranges for various PUR components and serves as a guide for material selection.
Note: The specified shore hardness ranges serve as guidelines for initial material selection. For the optimal design of a PUR component, additional factors such as workpiece weight, machine speed, dynamic loads, media used, and ambient and operating temperatures must be taken into account. Even minor changes in operating conditions can influence the required hardness and, consequently, the function, wear behavior, and service life. Therefore, the final material selection should always be based on the specific application.
The influence of Shore hardness on service life and component performance
Shore A hardness is not just a laboratory value; it determines whether a PUR component will perform its function reliably over the long term. Incorrect design can significantly impair performance, service life, and process reliability. If the shore hardness is chosen too low, the component will deform more than intended under load, which can lead to a loss of dimensional accuracy and functionality. In the case of rollers, there is also the risk of material transfer: the medium or coating adheres to the polyurethane instead of being transferred to the desired substrate in a controlled manner. Furthermore, the risk of material fatigue, cracking, and premature wear increases.
Conversely, if the shore hardness is too high, the necessary elasticity is often lacking. The contact area becomes smaller, the damping effect decreases, and rollers may be prone to slippage. Buffers and damping elements absorb loads less effectively, while higher surface pressures can cause scratches, grooves, or other damage to sensitive mating materials. At the same time, the stress on bearings, shafts, and machine components increases.
Another important factor is temperature. Polyurethane becomes softer as temperatures rise. For applications with continuous temperatures above 80 °C, an appropriate hardness reserve should therefore be factored into the design. Depending on the application, the PUR materials used by INTERNORM are designed for continuous operation at temperatures of up to 135 °C.
Regardless of the chosen shore range, polyurethane is characterized by high wear resistance. Compared to many conventional rubber materials, PUR can achieve up to 50% higher abrasion resistance. To evaluate these properties reliably and continuously improve them, we conduct standardized abrasion tests according to DIN 53516 as part of our quality assurance and material development processes. This procedure determines material loss under defined test conditions and enables an objective comparison of different material grades. The results flow directly into the selection and optimization of our PUR systems, helping to sustainably increase the service life of our components.
Conclusion: The right shore hardness makes the difference
For polyurethane, shore hardness is the key lever for the functional reliability, service life, and performance of a PUR component. The Shore A scale is relevant for most cast polyurethane components. It covers the range from 10 to 95 Shore A and is suitable for rollers, wheels, buffers, damping elements, and technical molded parts. Shore D, on the other hand, is primarily used for very hard plastics and TPU injection-molded parts.
The optimal hardness always depends on the specific application. Key factors include the component category, mechanical load, ambient temperature, and the properties of the mating material. Only by taking these factors into account can the desired function be ensured over the long term.
At INTERNORM, we manufacture polyurethane components for a wide range of applications—from rollers and wheels to buffers and custom molded parts. With a hardness range from 10 to 95 Shore A, we offer one of the broadest spectrums available and provide support in selecting the optimal material solution.
Conclusion: The right shore hardness is the foundation for a durable and high-performance PUR component.
FAQ
Here you will find direct answers to frequently asked questions about food grade plastic.
What is the Shore A hardness of polyurethane?
Polyurethane (PUR) processed via casting is available in a very wide Shore A range: from Shore A 10 (extremely soft, foam-like) to Shore A 95 (almost like hard rubber). The exact hardness depends on the polyol-isocyanate formulation and the processing temperature. INTERNORM produces PUR components across this entire range.
Shore A or Shore D — which applies to PUR components?
For cast PUR components, Shore A almost always applies—this range covers rollers, wheels, buffers, seals, and molded parts. Shore D is only relevant for very hard plastics or TPU injection-molded parts. The two scales cannot be converted into one another linearly—always check comparison values on the same scale.
What is the Shore hardness of polyethylene?
Polyethylene (PE-HD) typically has a Shore D hardness of 60–65. PE is not an elastomer but a semi-crystalline thermoplastic—Shore D is the appropriate measurement scale here. Cast PUR components fall within the Shore A range, making them significantly more elastic and abrasion-resistant than PE components of the same hardness.
