The real star of the plastics industry in the 1930s was "polyamide (PA)", far better known by its trade name, "nylon". Nylon was the first purely synthetic fiber, introduced by Du Pont Corporation at the 1939 World's Fair in New York City.

In 1927, Du Pont had begun a secret development project designated "Fiber66", under the direction of a Harvard chemist named Wallace Carothers. Carothers had been hired to perform pure research, and not only investigated new materials, but worked to understand their molecular structure and how it related to material properties. He took some of the first steps on the road to "molecular design" of materials. His work led to the discovery of synthetic nylon fiber, which was very strong but still very flexible. The first application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularly silk stockings.

It took Du Pont twelve years and $27 million USD to refine nylon and develop the industrial processes for its manufacture in bulk. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation that was called "nylon mania".

Nylon mania came to an abrupt stop at the end of 1941, when America entered World War II. The production capacity that had been built up to produce nylon stockings, or just "nylons", for American women, was taken over to manufacture numbers of parachutes for fliers and paratroopers. After the war ended, Du Pont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering off "nylon riots".

Nylon still remains an important plastic, and not just for use in fabrics. In its bulk form it is very wear-resistant, and so is used to build gears, bearings, bushings, and other mechanical parts.