durometer

Durometer is a device used to measure the hardness of polymers, elastomers, and some plastics by applying a standardized force with a calibrated indenter and measuring the resulting depth of penetration. The reading is expressed on scale numbers, the most common being Shore A and Shore D. Shore A is used for softer elastomeric materials such as many rubbers and flexible polymers, while Shore D covers harder plastics and harder elastomers. Other scales in less frequent use include Shore 00 for very soft materials and additional scales for specialized applications.

The measurement method involves pressing the indenter into the material under a fixed force for a specified dwell time, then translating the depth of indentation into a hardness value on the chosen scale. Higher numbers indicate harder materials. The technology is standard across many industries, and readings are governed by established test methods such as ASTM D2240 and ISO 7619/868, which specify apparatus, indenter geometry, force, dwell time, and conditioning.

Several factors can influence results, including surface texture, sample thickness or unsupported area, temperature, humidity, and the rate of indentation. Samples should be conditioned to a standard temperature and tested on a flat, smooth surface for repeatable results. Durometer readings are most useful for comparative quality control and material selection; they do not directly measure other mechanical properties such as modulus, and correlations vary with material type, geometry, and testing conditions.