Shore hardness — while it may initially seem like a purely technical term — relates to a very practical issue: how resistant a given material is to pressure. Is it soft like foam, or hard like the casing of a device? Measuring hardness using a Shore durometer provides a quantifiable and comparable answer to this question. Albert F. Shore developed the method, which remains one of the fundamental tools in materials engineering today — especially when working with plastics, elastomers, rubber, and other non-metallic materials.
Thanks to the Shore hardness scale, engineers and designers can determine whether a material meets the requirements of a specific application — whether it needs to be flexible, rigid, or resistant to compression or impact. The Shore scale is crucial for evaluating the hardness of polymeric, rubber, and silicone materials, as well as other non-metallic substances. Shore hardness is measured not only in laboratory settings — it’s a practical tool used in day-to-day operations across many industries where the appropriate hardness of polymer and silicone materials is critical.
What is the Shore hardness scale?
Shore hardness refers to a material’s resistance to indentation by a specific probe. To measure Shore hardness, a device called a durometer — or Shore hardness tester — is used. The deeper the probe penetrates the surface, the softer the material is, and vice versa. The measurement is expressed on a scale from 0 to 100, where 0 represents maximum softness, and 100 indicates very high hardness.
The Shore scale covers a wide range of materials — from ultra-soft gels to rigid plastics. By selecting the appropriate version of the scale, we can reliably test the hardness of
Durometer Types — measuring Shore hardness
A durometer displays the Shore hardness value, which can be compared against reference charts for rubber or plastic materials.
The Type A durometer is the most commonly used tool for measuring the hardness of medium-hardness rubber and elastomers. However, there are other scales designed for specific applications.
For example, Type C is used to measure the hardness of thin-walled rubber and films, while Type D is suitable for hard plastics. It’s worth noting that the Type C durometer is particularly useful for specialized materials where the Type A scale does not offer sufficient accuracy.
Shore hardness scale – types A, D, and 00
Hardness should be measured using the appropriate Shore hardness scale — typically Type A, D, or 00 — depending on the characteristics of the material. For more rigid materials, a Type D durometer is used, while extremely soft gels are measured with a Type 00 durometer. The choice depends entirely on the material’s hardness range and its intended application.
Thanks to standardized rubber hardness charts, it’s easy to compare different values and select the right material:
Shore hardness scale | Application |
Shore A | Soft rubber, elastomers, silicones |
Shore D | Hard plastics, rigid elastomers |
Shore 00 | Very soft gels and foams |
Shore C | Thin films, thin-walled rubber, latex materials |
The different types of Shore hardness scales were developed to better match measurement techniques to the characteristics of various materials. The hardness of rubber and silicone products typically falls within the range of 20 to 90 Shore A units (though some sources specify a range from 10 to 90 ShA, and up to 100 units for Type D). For technical materials with a hardness of 90 ShA, the Type A scale is already being used at the limit of its precision.
Type A is most commonly used to measure the hardness of rubber products, silicones, and elastomers, while Type D is applied for assessing rigid materials such as polycarbonates and nylon. Type 00 is designed for ultra-soft materials—such as foams and gels used in medical applications.
Using the appropriate Shore scale ensures accurate determination of a material’s hardness and its suitability for specific applications. This is essential in industries such as automotive, electronics, and healthcare.
How is material hardness measured? Shore hardness standards
Shore hardness is typically measured using a durometer, in accordance with standards such as ASTM D2240 and PN-ISO 868. The appropriate Shore scale — Type A, D, or 00 — is selected based on the material’s properties.
A Type A, D, or 00 durometer measures the force required to press a standardized indenter into the material. The choice of scale must match the characteristics of the sample. For flexible materials like elastomers, a Type A durometer is most suitable. For rigid materials (e.g., engineering plastics), a Type D durometer provides more precise data. Extremely soft gels are tested using a Type 00 durometer.
Proper hardness testing should take the following into account:
- Minimum sample thickness of 6 mm.
- Stabilized temperature during measurement.
- Flat, stress-free surface.
- Calibration of the durometer.
This is particularly important when making comparisons or analyzing situations where Shore hardness values must be correlated across different types of materials — for example, comparing an elastomer rated at 60 ShA with a rigid plastic rated at 70 ShD.
Keep in mind: the Shore hardness test is not just a measurement — it’s also a functional analysis, comparing material performance against operating requirements and resistance characteristics.
How to interpret values on the Shore A hardness scale?
Measuring the hardness of flexible materials using the Shore A scale is a fundamental tool for selecting the right product for a specific application.
The Shore hardness test, performed with a Type A durometer, assesses how resistant a material is to indentation — an indicator that directly reflects its performance in real-world use.
We’ll present examples of materials from AG TermoPasty along with their corresponding Shore A hardness values.
Hardness 10–30 ShA – very soft materials
Silicone Potting Compound 037, with a Shore A hardness of 12, is a low-hardness material known for its high elasticity and transparency. These properties provide excellent vibration damping and moisture protection, which are critical in LED applications. Measuring hardness with a Type A durometer in this range allows for a precise determination of softness — an important factor in evaluating the durability and performance of potting compounds.
Hardness 30–50 ShA – moderate hardness
An example is Silicone Potting Compound 011, with a Shore A value of 25. This is a moderately hard, flexible material that conforms well to irregular surfaces, offering effective protection for delicate sensors and circuitry. Using the Shore hardness scale enables precise assessment of elasticity and mechanical resistance — key aspects when testing the hardness of elastomers and rubber materials.
Hardness 50–70 ShA – higher shore hardness
Silicone Potting Compound 029, with a Shore A hardness of 63, is an example of a higher-hardness material, offering good mechanical stability and a thermal conductivity of approximately 2 W/mK. These properties are essential for protecting industrial electronics, where Shore hardness testing helps assess a material’s resistance to vibration and overheating.
Keep in mind: The typical range for high-quality technical silicones — those that balance mechanical strength with moderate elasticity — is 60–70 ShA. This level of hardness is recommended for components subject to repeated mechanical stress.
Hardness 90–100 ShA – maximum hardness on the A scale
Epoxy Potting Compound 141, with a Shore A value of 95, is an exceptionally hard material, approaching the hardness of some metals. It provides top-level mechanical and chemical protection and is used in applications such as power systems and power supplies. Measuring rigid materials with a Type A durometer in this range is crucial to ensure complete stiffness and mechanical durability — key to long-term product reliability.
Note: A Shore A hardness of 90 indicates a very rigid material — positioned at the upper limit of the A scale. In such cases, it may be useful to employ an alternative measurement method, such as the Shore D scale.
Some technical plastics can reach these values (90–100 ShA or 40–50 ShD), exhibiting mechanical properties that closely approach those of metallic materials. That’s why understanding and correlating Shore hardness values across different scales is essential.
Shore A hardness scale — is it the best choice?
It’s important to note that Shore hardness is just one of several methods for measuring material hardness. Other common techniques include:
- Brinell hardness,
- Rockwell hardness,
- Vickers hardness,
These methods are typically used to assess the hardness of metallic materials and differ in both measurement principles and the type of indenter used for compression or penetration.
Shore hardness testing is based on measuring a material’s resistance to penetration by a spring-loaded indenter. It provides a fast and repeatable result — especially useful for soft and flexible materials. Unlike metal hardness tests, which rely on the impression left by a ball or cone under load, the Shore durometer is lightweight and portable, making it ideal for testing the hardness of non-metallic materials such as rubber, elastomers, silicones, and foams.
Shore hardness in practice – the significance of the Shore hardness scale
The Shore hardness scale has broad applicability and plays a vital role across multiple industries where measuring the hardness of flexible and rigid materials is essential:
- Automotive – Rubber gaskets, vibration dampers, and other rubber components whose Shore hardness directly affects performance and effectiveness.
- Electronics – Silicone and epoxy potting compounds used to protect printed circuit boards (PCBs). Here, hardness testing with a durometer is crucial to evaluate mechanical and thermal resistance.
- Medicine – Silicone parts and orthopedic gels, where Shore hardness determines product comfort and usability.
- Consumer Appliances – Flexible casings and shock absorbers, where the Shore method is used to select materials resistant to wear and mechanical damage.
- Energy Sector – Components requiring high Shore hardness and chemical resistance, where Shore testing is a key factor in choosing suitable insulating materials
Why is Shore hardness testing so important?
Evaluating material hardness using a durometer enables designers and engineers to develop products that are more durable, reliable, and safe. By testing materials across different Shore hardness ranges (Types A, D, or 00), we can:
- Determine the appropriate hardness and flexibility of a product.
- Plan manufacturing processes that reflect the material’s mechanical and chemical properties.
- Correlate Shore hardness values with the product’s functional performance under real-world conditions.
The use of a Type A durometer for measuring the hardness of rubber and elastomers is a well-established standard in industries where test accuracy and repeatability are essential for quality control.
The importance of hardness testing in material quality control
Shore hardness testing plays a vital role not only during the design and material selection phases but also in the quality control of finished products. Regular Shore hardness measurements using a durometer help detect potential manufacturing deviations and ensure consistent mechanical properties.
When testing both flexible and rigid materials, using a Type A or D durometer provides a quick and accurate way to determine whether a material meets standardized hardness specifications. Standards such as ASTM D2240 and PN-ISO 868 outline precise guidelines for conducting these tests, ensuring reliability and repeatability of results.
Summary
Shore hardness testing and durometer measurements form a cornerstone of materials engineering. Selecting the appropriate Shore scale and using a durometer enables the evaluation of functional properties in both flexible and rigid materials. Whether low Shore hardness (20–30 ShA) or high hardness (90–100 ShA), each can be advantageous depending on the application context.
At AG TermoPasty, we place great importance on accurately determining the hardness of the materials we offer. If you require a material with a specific Shore hardness — such as 60–70 ShA or 100 units for a potting compound with the right firmness — feel free to contact us. We’ll help you choose the ideal product for your application, drawing on our expertise in rubber, elastomer, and resin hardness.
With the Shore hardness scale, we’re able to develop products that not only meet industry standards, but more importantly, deliver real protection and support for modern technological solutions.