Crazing

Many amorphous plastics show a whitening in some areas during stretching, known as stress whitening or crazing. This creates microscopically small areas, bridged by extremely stretched strands of material (crazes), which represent pre-damage and can indicate the beginning of a fracture.

Although normally undesirable, stress whitening in impact-modified plastics can be used to absorb energy and thus prevent fractures or allow further stretching. This phenomenon is also used in labelling devices to create contrast by stress whitening through targeted overstretching, while individual letters and numbers are embossed into a plastic adhesive strip.