ISO 12625-4:2016 specifies a test method for the determination of the tensile strength, stretch at maximum force and tensile energy absorption of tissue paper and tissue products. It uses a tensile-testing apparatus operating with a constant rate of elongation. It also specifies the method of calculating the tensile index and the tensile energy absorption index. In cases where impurities and contraries have to be determined, ISO 15755[6] applies for these detections in tissue paper and tissue products.