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Hardness standards for thermoplastic elastomers

A clear view through the jungle of standards

Josef Neuer, Head of Product Management EMEA at KRAIBURG TPE, provides information about different hardness standards and the process of standardization. What standards are there today and which ones apply specifically to thermoplastic elastomers? What needs to be considered?

In children's toys, as seals in storage boxes or as technical components - we encounter thermoplastic elastomers (TPE) in many everyday applications. Their particular strength? The combination of elasticity and thermoplastic processability. Decisive for a successful end product? Choosing the right hardness.

But how do you actually measure the hardness of TPEs? Which standards apply? And where are the pitfalls? In this article, Josef Neuer, Product Manager EMEA at KRAIBURG TPE, gives you an overview of a topic that is relevant for developers, quality assurance and production.

A brief look back

The history of measuring the hardness of elastomers began back in 1953 with DIN 53505, when a systematic standard for measuring the hardness of rubber and elastomer materials was defined for the first time.

In the meantime, a comprehensive system of standards has developed from this, which has been summarized in ISO 48 Parts 1 to 9 since 2021 - including ISO 48-4 for Shore A and D measurement, which plays a central role in our everyday work with thermoplastic elastomers.

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Why standards are important

Standards ensure comparability and reliability. A 70 Shore A material must show the same measurement result for the manufacturer as for the processor and customer.

The ISO 48 series offers exactly that: clear specifications for test conditions, equipment and measuring times - whether on the standard-compliant test specimen or directly on the component. Important to know: The measuring time for Shore measurements on TPE was extended from 3 to 15 seconds as part of the introduction of DIN ISO 7619-1 and the discontinuation of DIN 53505 in Germany in 2012.

As a result, TPE products appear slightly “softer” compared to before, although the material formulation has not changed. A detail that is often overlooked in practice - with potential effects on specifications and component drawings.

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Here is an overview of the current and previous standards for hardness measurement:

ISO 48-1 formerly ISO 18517
ISO 48-2 formerly ISO 48
ISO 48-3 formerly ISO 27588 (VLRH)
ISO 48-4 formerly ISO 7619-1 (Shore A and D)
ISO 48-5 formerly ISO 7619-2
ISO 48-6 formerly ISO 7267-1
ISO 48-7 formerly ISO 7267-2
ISO 48-8 formerly ISO 7267-3
ISO 48-9 formerly ISO 18898

Pitfalls and tips

Despite harmonization of standards, two stumbling blocks remain:

Outdated standard references: ISO 48 used to stand solely for IRHD hardness. Older drawings could incorrectly require a hardness test according to IRHD, although today, for example, Shore A is meant.
Transition areas: There is no simple conversion between hardness scales such as Shore A and Shore D. Special care is required in these zones - sometimes a double test with both types of method settings make sense.

The standard standard for measuring the hardness of thermoplastic elastomers is ISO 48-4. It is standard on the market, widely accepted and compatible with a large number of measuring devices. ISO 48-3 (VLRH, very low rubber hardness) is also used for very soft TPE types in particular - for Shore values below 10 Shore A.

Another exciting aspect is the technical evolution: from simple, mechanical hand-held measuring devices to fully automated, robot-supported test benches. Today, these enable highly reproducible results - with minimal operator influence and high efficiency. The hardness of a material is therefore more than just a number. It is the result of a regulated, standardized test procedure - and an essential quality feature.

At KRAIBURG TPE, we measure and test all raw materials and finished products in our in-house, accredited laboratory.

We are happy to support customers and processors with know-how, test data and insights directly from our laboratory.

Gain insights from the Experts

How to measure the hardness of a vulcanized or thermoplastic elastomer.

What does a typical hardness measurement according to ISO 48-4 look like in our company? What needs to be observed? Which steps must be followed and which specifications must be met? We have recorded a measurement for you in our application video. Find out more about the basics of hardness measurement here.

Watch video about hardness measurement