This European Standard specifies a method for the measurement of the strain hardening modulus which is used as a measure for the resistance to slow crack growth of polyethylene. The strain hardening modulus is obtained from and true stress versus draw ratio curves on HDPE geosynthetic barrier samples. This standard describes how measurement is performed and how the strain hardening modulus is determined. Details of the required equipment, precision and sample preparations are given. The method is valid for all types of polyethylene, independent from the manufacturing technology, comonomer and catalyst type.