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Durometer Testing

The durometer is the international standard for the hardness measurement of rubber, plastic, foam, gels, and other non-metallic materials. Rex Gauge has manufactured precise, durable durometers for over 70 years - they are recognized as the world leader in this field. All their products are made in the USA. All durometers and test block kits are normally in stock for immediate delivery. All Calibration Certificates are NIST-traceable.

Durometer testing is described in ASTM D2240. Except where noted, all these gauges comply with this Standard. Type A is used for soft rubber, plastics, elastomers, and printers’ rolls; type D is for hard rubber, rigid thermoplastics, floor coverings, fiberglass, and similar materials.

Durometers determine hardness by measuring the penetration of an indentor into a specimen. This can amount to as much as .100″, (2.5 mm); be sure your specimen is thick enough to preclude any chance of the indentor sensing the hardness of an underlying surface. Low durometer materials should be at least .250″ (6 mm) thick; thinner high durometer sample pieces can be tested accurately because the anvil penetrates less deeply. If your material samples are stackable, layer several of them to achieve the minimum required thickness.

For materials as thin as .050″ (1.25 mm), the Rex Type M Micro-A Durometer is recommended where samples cannot be stacked, or when only an individual specimen is available for testing. Again, materials thinner than .050″ which are stackable can be layered to achieve the minimum thickness required.

Additionally, the sample size must be large enough to ensure sufficient material surrounds the indentor's test point - we recommend a minimum specimen size of one inch square or round, with the test location on center.

The durometer hardness test can be used to indirectly measure other material properties, such as tensile modulus, resilience, plasticity, compression resistance, and elasticity – a set of material specimens is first tested on a standard tester for the property of interest, following which durometer readings are recorded on the same samples. The correlation for many properties is strong enough to allow monitoring by only durometer testing thereafter.