Durometer Hardness

ASTM D2240

Durometer Hardness Testing

The purpose of hardness testing is to measure a material’s resistance to localized and permanent deformation. Durometer hardness testing uses a particular tool, called a durometer, to gather and quantify hardness data.


The applications for durometer hardness testing are virtually limitless. Durometer hardness testing can be used to quantify many types of materials, ranging from very soft to very firm to the touch. Durometer hardness testing is commonly used to evaluate vulcanized rubber materials and products, thermoplastic elastomers (TPE), and elastomeric materials. This method can also be used to evaluate certain types of plastic.

Durometer hardness testing offers a surprising amount of nuanced insight into product performance. Hardness is not, as some might suspect, a measure of durability or how long a material will last. Rather, hardness testing can assess whether the appropriate degree of hardness has been achieved for the application. For example, the sidewall of a tire experiences a lot of flexing while in service and thus must not be too hard to bend and flex. Alternatively, a tire tread must be soft enough to grip the road surface, but if the material is too soft, the tread will wear down over time. Durometer hardness testing can help manufacturers identify the ideal hardness value for each unique material and application.

Durometer hardness testing is an incredibly valuable and important tool and is used in virtually every application and industry to assess materials and products. However, it’s worth noting that there is no simple relationship between the different types of durometers and rubber hardness scales, nor is there black-and-white criteria for choosing one hardness scale over another when testing. This is not a shortcoming of the methodology, but simply a reflection of the differing needs of each industry, material, and application. Durometer hardness testing is most valuable when used for control and benchmarking purposes and for understanding a material’s general feel. Data gathered from two different hardness assessment methods should not be compared, since the relationship between the two sets of data will not be relevant.


ASTM D2240 is a standardized durometer hardness testing method that describes methods for twelve different types of durometers. Each durometer has a unique combination of diameter, extension, and spring force. Additionally, the shape of the presser foot can differ between durometers, ranging from cones, truncated cones, and conical points to spherical radii and radius disks.

Samples prepared for most ASTM D2240 testing must be at least 0.24 inches thick, though some durometers can assess materials that are just 0.05 inches thick.

To conduct the test, the sample is placed on a hard, flat surface. The durometer is applied firmly and consistently to the sample for a specified period of time, usually one second. The pressure is steady, not sudden or aggressive. After the elapsed time, the durometer is read to discern the material’s hardness value.

The durometer will report a different hardness reading depending on the time elapsed. For example, a three-second reading will differ from a five-second reading. For this reason, it is critical to observe the same timeframe for each related test to ensure consistent data.

Limitations of ASTM D2240

ASTM D2240 is not appropriate for measuring the hardness of coated fabrics or coated materials. This is largely due to the fact that the coating interferes with accurate measurement of material hardness. It may be possible to use the methods outlined in ASTM D2240 to measure the hardness of the coating itself, but the coating would need to be separated from the base material to ensure accurate data and must meet the minimum thickness requirements outlined in the standard. ASTM D2240 is also not appropriate for coated fabrics.

Additionally, ASTM D2240 should not be considered analogous to ASTM D1415. ASTM D1415 uses a rigid ball, rather than a durometer to measure hardness. While both methods have value, they should not be considered interchangeable.

Durometer Hardness Testing from ACE Laboratories

ACE Laboratories has the instrumentation and in-house expertise to support your durometer hardness testing needs, from research and development to final product validation. Our experts can help you choose the appropriate rubber hardness scale and type of durometer for your application and provide valuable interpretation of hardness testing data, so you can make confident decisions about your product or material.

Our experts have years of combined experience in both testing labs and hands-on industry environments, so we understand the real-world and business implications of durometer hardness data and how it affects material and product performance. We’re also proud to offer the fastest turnaround times in the industry, so you can maintain your ambitious production goals and stay ahead of your competition.

To learn more about durometer hardness testing or get started on a testing project, talk to a member of our team >

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