Compression set testing is used to determine an elastomer’s ability to maintain elastic properties after prolonged compressive stress. The test measures the amount of permanent deformation that occurs when a material is compressed to a specific deformation, for a specified time, at a specific temperature. This permanent deformation is of particular concern when elastomers are used to create seals, as decreasing seal force has the potential to create leaks over time.

Compression set testing is performed using short cylinder or disc shaped samples. Prior to testing, the thickness of the specimen is measured. The specimen is then placed in the compression device with spacers to ensure 25% compression and placed in the testing environment. After removing the sample from the testing environment, the specimen is allowed to cool for 30 minutes before measuring the final thickness. The compression set measurement is the difference between the original thickness of the specimen and the thickness after test, expressed as a percentage. The lower the percentage, the better the material resists permanent deformation under a given deflection and testing environment.

Keywords: ASTM D395, ASTM D1414, compression, compression set, permanent deformation, seal force