Compression set

This has the formal name compression set under constant force in air. In compression set A a force of 1.8 kN is applied to the specimen for a set time at a set temperature. Compression set A is defined as the percentage of original specimen thickness after the specimen has been left in normal (uncompressed) conditions for 30 minutes. C_A, the compression set A is given by C_A = [(t_o - t_i) / t_o] * 100 where t_o is the original specimen thickness and t_i is the specimen thickness after testing.^[2]

This has the formal name compression set under constant deflection in air. The specimen is compressed to 75% of its original height for a set time and at a set temperature (sample is compressed to .75 of its original height). Compression set B is (like Compression set A) defined as the percentage of specimen deflection after it has been left in normal (uncompressed) conditions for 30 minutes. C_B, the compression set B is given by C_B = [(t_o - t_i) / (t_o - t_n)] * 100 where t_o is the original specimen thickness, t_i is the specimen thickness after testing and t_n is the spacer thickness or the specimen thickness during the test.^[2]