AbstractIgepal assisted environmental stress cracking (ESC) of LDPE has shown three characteristic regions with increasing crack driving force: Region I‐crack speed and craze length increased. Region II‐crack speed and duplex plastic zone length were constant, and Region Ill‐crack speed decreased while the deformation zone length increased. The activation energies for the three regions were 100, 23, 20 kJ/mole, respectively. The proposed rate controlling processes of ESC for the LDPE/Igepal system are: Region 1 is controlled by a;‐relaxation, and Region II and III are controlled by lamellar orientation. The Igepal plasticizes the amorphous phase and facilitates the stress induced orientation of the lamellar.