This International Standard specifies a method for determining the loss in thickness of flexible cellular materials when compressed repetitively to a fixed level of strain. It is particularly useful for quality control in the manufacture of flexible polymeric cellular materials. Another procedure already exists as ISO 3385: this measures the fatigue characteristics of flexible polymeric cellular materials by constant-stress loading of the specimen rather than constant strain. It forms the basis of a material classification system in ISO 5999. These two fatigue procedures are complementary to each other and can both be useful in the prediction of end-use performance. The procedure and equipment used in this International Standard allow testing of a large number of test pieces at any one time, whereas ISO 3385 only allows testing of one test piece at a time under the compression device.