ISO 815 Test Standard Explained

Compression Set - ISO 815

The permanent deformation remaining after release of a compressive stress. Compression set is expressed as the percentage of the original deflection. Compression set is an important property for elastomers and cushioning materials.

The test specimen is compressed for a specified time at a specified temperature. Compression set is calculated as the percentage of the original deflection after the material is allowed to recover at standard conditions for 30 minutes. Compression set is calculated using the formula:
C = [(h_o - h_i) / (h_o - h_n)] * 100
where h_o is the original specimen thickness, h_i is the specimen thickness after testing, and h_n is the spacer thickness.

Compression Set Testing

Three different strains may be used for testing. The strain used depends upon the hardness of the material. IRHD stands for International Rubber Hardness Degrees (see ISO 48).

Two different specimens may be used for testing. Test specimens are cylindrical disks cut from a slab of the testing material.

Similar Standards

• ASTM D395

Property information for specific grades of resin are available in the Prospector Plastics Database.