What is shore hardness and how is it measured?

As a Purchasing Manager, Product Designer or Product Engineer, you understand the pivotal role that identifying the optimal shore hardness of silicone rubber plays in the product development process. Drawing upon our expertise in silicone rubber extrusions and a multitude of previous applications, we can help you determine the appropriate shore hardness for your application.
Through this blog, we bring you real world insights and address all of your shore hardness related questions, including:

  • What is the shore hardness scale?
  • Why is measuring shore hardness integral to the manufacturing of silicone rubber extrusions?
  • How is shore hardness measured?
  • What does shore A hardness mean and what is shore D hardness?
  • Which shore hardness is best suited to which specific application?

What is the shore hardness scale?

The shore hardness scale, often referred to as the durometer scale, is a measure of a material’s resistance to indentation or, more to it more simply, how ‘hard’ it is. Primarily used for assessing the hardness of elastomers like silicone rubber, the scale was devised by Albert F. Shore, from whom it derives its name.

The scale is divided into different types (levels), such as shore A, shore B, shore C and shore D, each measuring the differing degrees of hardness of different materials. The shore type is preceded by a numerical value indicating the level of hardness to a precise degree, ranging from 0-100, with higher values indicating a harder material​​. For example, marshmallows have a hardness level of 10 Shore A whilst hard hats have a hardness level of 80 Shore D.

The shore hardness scale is widely utilised in manufacturing, engineering and product development to assess the suitability of materials for various applications.

See our silicone rubber technical datasheet, including shore hardness details and their intended applications

Why is measuring shore hardness important during the silicone rubber extrusions manufacturing process?

Measuring shore hardness is a crucial stage of the silicone rubber extrusion manufacturing process for several reasons:

Product performance

Silicone rubber shore hardness influences the performance of your extrusion, directly impacting the success of your finished product. If your desired application demands flexibility, compressibility, or some rigidity, selecting the right shore hardness ensures that the silicone extrusions will function optimally under the expected conditions.

Sealing and insulation

In applications where your extrusions are used for sealing or insulation, selecting the right silicone rubber shore hardness is critical to achieving an effective seal and ensuring a reliable insulation. For a solid silicone rubber extrusion, grades with a softer shore hardness are chosen for a compressible sealing product, but for those profiles with a hollow, they can often be compressed to seal without dropping the shore A value.

Ease of installation

Depending on the application, silicone rubber extrusions may need to be flexible enough for easy installation while still maintaining the required level of hardness for functionality. Many of the silicone rubber profile rings that we manufacture are supplied as a slight stretch fit for optimal operator performance, the grades with a softer shore hardness have a higher elongation, and therefore finding the optimal balance between these two figures can lead to a successful product.

Cost efficiency

Selecting the appropriate shore hardness helps to avoid over-engineering your extrusions or manufacturing extrusions that under-perform, which can lead to unnecessary material and prototyping costs or product failure.

How is shore hardness measured?

Shore hardness is determined using a tool known as a durometer, which uses standardised techniques for gauging the hardness of silicone rubber and other elastomers. The numerical values assigned by durometers offer a relative assessment of hardness, allowing for comparisons between different yet comparable materials measured using the same durometer device, scale and measurement standard.

Conducting a shore hardness test involves using a durometer gauge equipped with a spring-loaded steel rod. This rod is pressed against the material’s surface, creating an indentation, with the durometer providing a reading based on this indentation.

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What is the difference between shore A and shore D hardness?

Shore A and shore D are two different scales which are popular within the rubber and plastics industries. The two key differences between shore A and shore D hardness are:

Material Type

Shore A is used to measure the hardness of softer materials, including flexible and elastic materials such as silicone rubber. It is commonly used for materials that have a significant degree of flexibility and deformation such as Silicone Rubber, EPDM and Fluorosilicones, Neoprene and Fluorocarbon elastomers. Shore D is designed for harder materials, including rigid rubbers, semi-rigid plastics and hard plastics.

Measurement Range

In comparing Shore A to Shore D scales, the shore A scale covers the lower range of hardness, starting from very soft and extends to materials with only a moderate degree of hardness. The shore D scale covers a higher range of hardness values that are more rigid and less flexible.

Which applications are best suited for which hardness levels?

Various applications demand distinct hardness levels, tailored to the specific mechanical properties required.

Very Low Shore Hardness (10 to 25 Shore A);
Materials which are very flexible, soft and compressible grades, highly suited as weatherproofing seals with solid cross sections, or often used in applications where a foam or sponge material can not be utilised.

Low Shore Hardness (25 to 40 Shore A):
Soft and flexible materials with low hardness are suitable for applications requiring high elasticity and deformation. Its flexibility makes it an excellent choice for applications where the extrusion is designed to function as a seal.

Medium Shore Hardness (40 to 65 Shore A):
Materials with medium hardness are used in applications where a balance between flexibility, compressibility and holding shape without collapsing is necessary, for example, tubing, profiles, autoclave seals. The medium shore hardness materials are the most frequently used materials in manufacturing, they have good mechanical properties and due to the ease of processing also can be supplied as complicated shapes.

High Shore Hardness (70 to 90 Shore A):
Harder materials are used in applications where firmness is important. These grades can support their own shape, are harder to compress, and possess lower elongation at break values. These harder grades are sometimes used in applications where a plastic component cannot be used, for example at high temperatures.

Very High Shore Hardness (60+ on Shore D Scale):
Extremely hard materials are suitable for applications demanding stiffness and resistance to deformation, such as rigid plastics.

While there are also other Shore hardness scales, these are used less often in the plastics and rubber industry.

Advanced materials shore hardness scale

Why is it important to get the right silicone rubber shore hardness for your application?

It is crucial to select the correct shore hardness for your application to get the best performance and material characteristics. Compressibility, elongation and flexibility all change in relation to shore hardness, so getting the correct balance contributes directly in determining successful sealing products.

Unsure of which silicone rubber shore hardness to designate for your application?

Our expert team at Advanced Materials is available to guide you in selecting the optimal shore hardness for your specific application.

Contact us today to speak with our specialists and request your sample pack of silicone rubber slabs with different shore hardness levels to support your decision making process.

Advanced Materials is a leading supplier of silicone rubber extrusions. To find out more about our silicone rubber manufacturing services contact our expert and friendly team on +44 (0)1903 713566 or sales@amsilicones.co.uk