A living hinge is formed when partially oriented polypropylene is cold drawn and flexed for the
first time, resulting in stretching ratios as high as 2 or 3 to 1. A tremendous increase in tensile
strength is then produced. Well-oriented webs have virtually unlimited fold endurance, assuming
the appropriate part design, resin, and molding conditions are utilized. Furthermore, they do not
stress-crack unless chemically attacked. Severe oxidizing environments (including direct
sunlight exposure) will degrade the service life of a polypropylene living hinge.