A cracking condition of the surface of rubber articles such as tires and footwear, resulting from constantly repeated bending or flexing in service.

Cracking in a film produced by repeated flexing. Flex cracking may occur over long distance shipping. Certain films are more flex crack resistant then others. The relationship between the shipping container and bag dynamics must also be taken into account when evaluating shipping methods. Form-Fit bags with metallocene based films (such as CDF's Flexus(TM) and higher temperature-resistant Flexus HF) and ASTM tested containers help reduce flex cracking related leakers.