Durometer

Durometer, in Czech called "Hardness Tester", is a device (note, sometimes the term "20 Durometers" is understood and may be used by some manufacturers even as a unit of hardness!) for measuring the hardness of very soft to very hard materials (depending on the scale and type). The device consists of an analog or digital display and a protrusion with a rounded tip.

Measurement is conducted by pressing the part with the tip onto the material being measured, causing the tip to sink into the surface of the material to a greater or lesser extent. The softer the material, the deeper the tip sinks (not punctures) into the surface and a lower value is displayed on the scale or display, most commonly in Shore units.

Which standards are used for modern Hardness Testers?

Currently, the following standards apply for testing materials (it is worth mentioning that it should be at least 6.4 mm thick / 0.25 inches):

• Type A – uses hardness and units in the range of 20-90 A and is tested on materials such as soft vulcanized rubber, natural rubber, nitriles, thermoplastics, elastomers, flexible polyacrylate, thermosets, waxes, leather, felt, …
• Type B (for things above 90 A and below 20 D) – slightly hard rubber, thermoplastic elastomers, paper products, fibrous materials, …
• Type C (things above 90 B and below 20 D) – medium hard rubber, thermoplastic elastomers, medium hard plastics, and thermoplastics.
• Type D (things above 90 A) – hard rubber, thermoplastics, elastomers, harder plastics, and rigid thermoplastics.
• Type DO (things above 90 C or below 20 D) - slightly hard rubber, thermoplastic elastomers, and very dense textile (bent) things.
• Type M – designed specifically for testing O-rings and thin pieces of rubber (the minimum thickness here is from 1.25 mm upwards).
• Type O (things below 20 DO) – soft rubber, thermoplastic elastomers, thermoplastics, extremely soft plastics, thermoplastics, and medium dense textile (bent) things.
• Type OO (things below 20 O) – extremely soft rubber, thermoplastic elastomers, sponges, extremely soft plastics and thermoplastics, foams, minimally dense textile (bent) things, human and animal skin.
• Type OOO – extraordinarily soft materials, such as construction material imitating open-cell foam.
• Type OOO-S – strongly soft things, such as open foam cells (lighter and air can get in) and closed foam cells (heavier and air cannot pass through).
• Type CF (ASTM F1957) – composite foam materials like car seat cushions, body-shaped plastic cushions, bulletin boards, seating linings, door panels, …