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What is a Durometer?
A durometer is an instrument for testing the hardness of various plastics & rubber. ASTM D2240 Standard Test Method for Rubber Property, Durometer Hardness. This test method covers twelve types of rubber hardness measurement devices known as durometers: Types A, B, C, D, DO, E, O, OO, OOO.

Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test.

ASTM D2240 durometers allow for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock, and measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6.4 mm (.25 inch) thick.

Durometer Type / Scale 
Typical Examples of Materials Tested 
Durometer Hardness 
Soft vulcanized rubber, natural rubber, nitriles, thermoplastic, elastomers, flexible polyacrylics, thermosets, wax, felt, and leathers.
20-90 A
 
Moderately hard rubber, thermoplastic elastomers, paper products, and fibrous materials
Above 90 A Below 20 D
Medium-hard rubber, thermoplastic elastomers, medium hard plastics, and thermoplastics.
Above 90 B Below 20 D
Hard rubber, thermoplastic, elastomers, harder plastics, and rigid thermoplastics
Above 90 A 
Moderately hard rubber, thermoplastic elastomers, and very dense textile windings.
Above 90 C Below 20 D 
Designed specifically for measuring small cross section O-rings and thin pieces of rubber (not less than 1.25mm thick).
Soft rubber, thermoplastic elastomers, very soft plastics, thermoplastics, and medium-density textile windings.
Below 20 DO 
Extremely soft rubber, thermoplastic elastomers, sponge, extremely soft plastics and thermoplastics, foams, low- density textile windings, and human & animal tissue.  
Below 20 O
Very soft materials, (e.g.) open cell foam.  
Type OOO-S Shore Durometer measures the hardness of viscoelastic polymers. Applications include motorcycle seats, medical pads and wheel chair cushions for pressure ulcer prevention. Equestrian pads, gun recoil pads and cool gel mattresses.
Composite foam materials, such as amusement ride safety ASTM F1957 cushions, vehicle seats, dashboards, headrests, armrests, and door panels.
ASTM F1957 
The Model 302SL Foam & Rubber Durometer is a unique instrument that measures the hardness of soft materials such as foam rubber, sponge rubber, cellular material and gel-like materials.
 

 

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