This part of ISO 22088 specifies a method for the determination of the environmental stress cracking (ESC) resistance of thermoplastics when they are subjected to a fixed flexural strain in the presence of chemical agents. ESC is indicated by the change of a suitably chosen indicative property of specimens that have been strained for a defined time in the environment. The method of test is suitable for determining the resistance of sheets and of flat test specimens, especially the sensitivity of localized surface regions of specimens, to ESC. The bent strip method is suitable for the determination of ESC caused by gases and liquids as well as solids containing migrating substances (e.g. polymeric adhesives and materials containing plasticizers) in contact with a specific polymer. Preferably, this method is used to determine the ESC resistance of rigid plastics that exhibit only moderate stress relaxation during the time of the test. This is essentially a ranking test and is not intended to provide data to be used for design or performance prediction. NOTE For a constant-strain test, refer to ISO 22088-5. For a constant-load test, refer to ISO 22088-2.