Mechanical & Physical Testing

Compression Set

 Properties Measured

Compression set evaluates a material’s ability to maintain elastic behavior after subjection to prolonged compression.  The value is related to sealing force retention and stress relaxation phenomenon.   Most typically measured for elastomers, but applicable to thermoplastics and other materials in certain cases.


Standard and custom button compression, constant deflection

Instrumented constant load testing

Standard testing in air

O-ring and custom specimen geometries

Testing immersed in fluids and/or gases

Testing at low temperature

Sample Requirements

Sample requirements vary by standard. The most common is ASTM D395 Method B, which requires buttons of 12.5 mm x 29.0 mm (0.49 in x 1.14 in) for Type 1 or 6.0 mm x 13.0 mm (0.24 in x 0.51 in) for Type 2 specimens. Plied (stacked) specimens cut from molded plaques, and o-ring specimens are also appropriate.

Typically a minimum of three specimens are measured.

Example Test Protocols


Standard Test Methods for Rubber Property – Compression Set

ASTM D1414

Standard Test Methods for Rubber O-rings

ISO 815

Determination of Compression Set

ISO 1653

Determination of Compression Set under Constant Deflection at Low Temperature

ASTM D1229

Standard Test Method for Rubber Property – Compression Set at Low Temperature

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