Examples of design modifications to eliminate or minimize distortion of plastic parts. (a) Suggested design changes to minimize distortion. Source: F. Strasser. (b) Die design (exaggerated) for extrusion of square sections. Without this design, product cross-sections swell because of the recovery of the material; this effect is known as die swell. (c) Design change in a rib, to minimize pull-in caused by shrinkage during cooling. (d) Stiffening the bottoms of thin plastic containers by the bottoms of thin plastic containers by doming-this technique is similar to the process used to make the bottoms of aluminum beverage cans