Plastic hardness testing: an overview of Shore test methods

Introduction: Hardness as a key value in plastics engineering

The hardness of a plastic describes its resistance to the penetration of a test body and is therefore an essential criterion when assessing mechanical properties. In practice, hardness determines how a component reacts to external load, whether it deforms, sinks in or remains dimensionally stable over a longer period. Particularly in industrial production, the hardness testing of plastics is a proven method for reliably assessing material quality before use.

Hardness tests are used when plastics are employed in safety-relevant or mechanically stressed areas – for example in housings, gears, seals or sliding surfaces. In material development, it serves as a control variable for optimising formulations or adjusting processing parameters. In many applications, the right hardness means a compromise between flexibility, durability and resistance to external influences.

Alongside tensile strength and impact strength, the material hardness of plastics is therefore a central characteristic value. In combination with density, modulus of elasticity or temperature resistance, it provides a comprehensive picture of the material's behaviour.

For technicians and developers, hardness testing is therefore not an isolated test value, but part of a holistic material characterisation. It also allows a quick and non-destructive assessment – a clear advantage over more complex mechanical test methods.

The hardness of a plastic describes its resistance to the penetration of a test body. It is an important characteristic value in the selection and quality assurance of materials, particularly for elastic and semi-rigid polymers.

The plastics hardness test provides quick and precise information on the suitability of a plastic for use in mechanically stressed applications. Alongside tensile strength and impact strength, the material hardness of plastics is a central criterion for avoiding deformation and material failure.

The Shore hardness test: principle and significance

The Shore hardness test is the most frequently used method for hardness measurement in polymers. It measures the depth to which a standardised indenter penetrates the material. The lower the penetration depth, the higher the Shore hardness. The method is used not only for elastic materials, but also for engineering thermoplastics, in order to objectively assess their mechanical properties.

The test is usually carried out in accordance with the standard DIN EN ISO 868. In international contexts, ASTM D2240 is also widely used.

Shore A vs. Shore D: differences and areas of application

Shore hardness is divided into two main scales, each of which is adapted to the hardness ranges of different plastics. Both test scales are based on the same measuring principle – the penetration depth of a standardised test body into the material to be tested – but differ in test force, shape of the indenter and area of application.

Shore A

This scale is specifically tailored to soft plastics and elastomers. These include materials such as:

• Thermoplastic elastomers (TPE)
• Soft PVC compounds
• Rubber-like materials
• Silicones and certain polyurethanes

The typical Shore A hardness ranges from 10 (very soft, roughly like gel material) to 95 (hard, but still indentable with finger pressure). The measurement is carried out with a lower test force and a blunter indenter, in order to be able to represent the behaviour of soft materials in a differentiated way. Shore A is the preferred value for components in which a certain elasticity is to be retained – for example seals, shock absorbers or grips.

Shore D

The Shore D scale is used when significantly harder plastics are involved. These include engineering thermoplastics such as:

• ABS (acrylonitrile butadiene styrene)
• PA (polyamide)
• POM (polyoxymethylene)
• PEEK (polyetheretherketone)

These materials exhibit Shore D values of around 30 (still flexible) to 80 or more (close to thermoset behaviour). The measurement is carried out with a higher test force and a pointed indenter, in order to determine the hardness of hard, tough plastics reproducibly. Shore D is suitable for components with high mechanical requirements, such as gears, housings or bearing bushes.

Practical relevance of the choice of scale

The choice of the right scale is decisive, since Shore A and Shore D are not directly comparable. A material with Shore A 95 can certainly exhibit similar properties to one with Shore D 40 – however, the measurement results are not transferable. In industrial practice, it is advisable to determine the scale on the basis of the expected hardness range and the material group. Modern test devices often offer both scales, in order to be able to efficiently capture transition ranges.

Anyone who selects the correct Shore scale in plastics testing lays the foundation for reproducible measured values, robust material comparisons and effective quality assurance. Particularly in the development of new compounds or in the specification of engineering components, this aspect should not be underestimated.

How the test is carried out

1. Prepare the test specimen (at least 6 mm thickness, flat surface)
2. Calibrate the test device
3. Place the indenter vertically
4. Read off the measured value after 1–3 seconds

The indentation test for plastics should be carried out at room temperature. Repeated measurements (at least 3 per point) ensure reliable mean values. Modern test devices for Shore hardness offer a digital display and automatic averaging.

Standards and test standards

Alongside DIN EN ISO 868, other relevant standards such as ASTM D2240 exist, which define similar methods. For transparent comparability in international supply chains, stating the standard in test reports is essential. In plastics engineering, these test standards are regarded as the basis for material selection in design and series production.

Typical Shore hardness values of plastics

Plastic type	Shore A	Shore D
TPE	40–80	-
Silicone	10–90	-
PE-HD (PE300)	-	60–65
PA6 (polyamide)	-	75–80
POM-C	-	80–84
ABS	-	70–78
PEEK	-	85–90

Note: The values can vary depending on filler content, processing and temperature. For reliable plastics characterisation, testing under defined conditions is advisable.

Test methods in comparison: Shore, Rockwell, Martens & more

Hardness testing for plastics is versatile – depending on the material type and application, different methods are used. Alongside the common Shore measurement, Rockwell, Martens hardness testing and ball indentation tests (Ballindentation) are also common methods used for harder or more brittle materials.

While Shore A and Shore D are particularly suitable for elastomers and thermoplastics, Rockwell and Martens also deliver robust results for fibre-reinforced or filled plastics.

Recommendation by material type:

• Elastomers, TPE, soft PVCs: Shore A
• Engineering thermoplastics: Shore D or Rockwell
• Reinforced plastics or thermosets: Martens or ball indentation method

The choice of method therefore depends not only on the material, but also on the intended use, the standards situation and the requirements for reproducibility and documentation.

Typical industries and fields of application

The hardness testing of plastics plays a central role in numerous industries:

• Automotive industry: e.g. seals, dashboards, mounts
• Medical technology: hoses, housings, flexible components
• Packaging industry: films, blisters, flexible containers
• Mechanical engineering: engineering semi-finished products, plastic gears, bearing parts
• Electronics: housings, insulators, flexible components

In each of these industries, hardness testing enables the targeted selection and verification of suitable materials.

Integration into test processes and quality assurance

The Shore hardness test is a fixed component of quality assurance in many operations. It can be integrated into existing test processes without difficulty – for example within the scope of incoming goods inspection, process monitoring or component approval. In conjunction with digital test devices, the measurement results can be automatically recorded, documented and evaluated. In this way, Shore tests contribute significantly to standardisation and traceability – particularly in series production.

Limits of and alternatives to the Shore test

Shore hardness provides no statement about the strength or toughness of a material. For hard plastics, it reaches its limits. In such cases, Rockwell hardness, Ballindentation or nanoindentation are used. These provide more differentiated results for brittle or high-strength polymers. Anyone who requires comprehensive plastics testing in accordance with standards should combine several methods depending on the application.

Relevance for practice

In series production, incoming goods inspection or material development, the Shore test is an efficient tool for quality assurance. It is used regularly, particularly for rubber parts, TPEs or housings made of engineering thermoplastics. For processors and developers, knowledge of hardness testing for plastics in accordance with Shore is indispensable in order to comply with specifications and avoid material defects.

Our range of services: plastics testing in accordance with Shore

We offer professional hardness testing of plastics in accordance with Shore A and Shore D in our test laboratory. Whether incoming goods inspection, material verification or development support – our test methods are standardised in accordance with DIN EN ISO 868 or ASTM D2240 and provide you with reliable characteristic values for your engineering plastics, elastomers or thermoplastic components.

Your advantages:

• Precise test reports with documented Shore values
• Fast turnaround times – also for series tests
• Personal advice on the interpretation of the measurement results
• Can be combined with other material tests

Contact us for an individual test or a tailor-made offer.

Indispensable method

Hardness testing in accordance with Shore is an indispensable method for assessing the mechanical characteristic values of plastics. The choice of the right scale, compliance with the test standards and an understanding of the material properties ensure reliable results. Anyone who wants to process, compare or specify plastics efficiently should keep a firm eye on Shore hardness as a test value. This lays the foundation for robust material decisions in an industrial environment.