Shore Durometer Solidity Testing: Understanding and Applying Foam Solidity Values

Measuring the solidity of a material is one of the most important testing areas for a product expected to perform in a range of applications. Given the different varieties of foam and the many uses for each, knowing a material’s solidity is useful in identifying which foam types work in some areas and which do not. This evaluation is performed for foam and foam rubber products by a Shore Durometers Durometer, which measures and assigns a value for the solidity of a tested material.

Invented by Albert F. Shore in the 1920s, the durometer is a dedicated instrument that measures the solidity (or Shore hardness) of a material based on its indentation strength. This is different than a material’s scratch resistance which is gathered by comparing two materials, one of which could or may not be controlled or have precise values. A durometer may vary in size, but most are generally hand-held elements. They have a precision dial or digital display that shows tellings and a small shaft that extends down to a flat bottom. Some newer durometers have minimized the presence of a shaft or eliminated it completely. Protruding from the bottom is a 2. 54 millimeter (. 100 inch) spring-loaded pin, with either a round or blunted cone-shaped point that records the measurements. Once rested against an object to be measured, the durometer is, in general terms, pushed downward through to the flat bottom of the shaft meets the surface of the material. Depending on the material’s solidity, the pin may be forced back into the shaft, as happens with hard materials, or indent the material, as occurs with softer products.

There are numerous scales on which values are measured because of the wide range of materials that can be assessed with a durometer, such as hard plastics, rubbers and foam. The three most utilized scales are “A, inch which covers the widest choice of materials but neither the softest nor hardest, “D, inch on which the hardest materials like plastics are recorded and “OO, inch for the softest materials like foams and rubbers. Regardless of the scale type used, rank values they fit on a statistical scale from 0 to 100, with 100 being the hardest, and 0 being the softest.

The majority of foam products that obtain durometer rating are ranked on the OO scale, as foam is one of the softer materials that can be tested with this process. This scale includes but is not limited to varieties like Minicel, Volara and neoprene. The ratings produced on the OO scale go from 0 to 100, as with all the others. But because the scales measure different products, an OO value cannot be evenly compared to a material measured on the A or D scale. The scales do loosely overlap, so while it is also possible that a high reviewing OO material is harder compared to a medium or low reviewing A or D material, the only way for a true comparison is to test the different materials on the same durometer scale. Different durometers are used for different scales as opposed to a single adjustable durometer because of the diversities in pin types and spring pressure.

The two real-life values that can be most directly assessed from this test are pressure resistance and material flexibility. However, when measuring foam and other soft products, it must be understood that a material’s thickness and the weight being supported have a large impact on its pressure resistance. For this reason, a durometer value should be seen as a starting point for expectations on how a product will perform, with an and the externalities impact a specific material’s performance in a given situation. For example, a higher valued material will be harder and better at resisting pressure compared to a lower value when both are measured similarly, but results may be different when using a low rated material at ten times the thickness of a higher rated material in the same application. And the harder a material is, the more unlikely that it is to be flexible without breaking. Some examples of where it is important to know a foam’s solidity include custom packaging and package inserts, components like industrial gaskets, construction materials like expansion joint filler and athletic equipment such as shoulder or shoulder pads.

When considering materials for any project, it is important to look at the full choice of product characteristics to make sure you ultimately choose the perfect material for your job. Shore solidity is one very useful rank and it can be used to help you produce an even more informed purchasing decision.

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