Stephanie L. Kwolek was a pioneer and a scientist:

Stephanie L. Kwolek, a DuPont chemist who invented the technology behind Kevlar, a virtually bulletproof fiber that has saved thousands of lives, died on June 20, 2014 in Wilmington, Del. She was 90.

The chief executive of DuPont, Ellen Kullman, announced the death, calling Ms. Kwolek, who spent 15 years in the laboratory without a promotion before her breakthrough, “a true pioneer for women in science.”

Kevlar is probably best known for use in body armor, particularly bulletproof vests. A DuPont spokeswoman estimated that since the 1970s, 3,000 police officers have been saved from bullet wounds through the use of equipment reinforced with Kevlar, which is far stronger and lighter than steel.

The product has found its way into all corners of the modern world. It has been used in car tires, boots for firefighters, hockey sticks, cut-resistant gloves, fiber-optic cables, fire-resistant mattresses, armored limousines and even canoes. It is used in building materials, making them bomb-resistant. Safe rooms have been built with Kevlar to protect a building’s occupants during hurricanes. Kevlar has been used to reinforce overtaxed bridges.

ts popularity has proved a windfall for DuPont. Kevlar has generated several billion dollars in revenue for the company. Ms. Kwolek did not directly benefit from it financially, however; she signed over patent royalties to DuPont.

The research that led to Kevlar began in the early 1960s, when women were a rarity in industrial chemistry. Ms. Kwolek was part of a team at DuPont’s research laboratory in Wilmington that was trying to develop a lightweight fiber that would be strong enough to replace the steel used in radial tires.

The work involved manipulating strings of carbon-based molecules to produce larger molecules known as polymers. At one point, in 1964, Ms. Kwolek was struggling to convert a solid polymer into liquid form and finding the results to be a murky disappointment. Instead of the clear, syrupy mixture she expected, the liquid was thin and opaque.

Ms. Kwolek’s peers suggested that the polymer she had concocted would probably not work as a fiber. But Ms. Kwolek persisted. She persuaded another scientist to “spin” the liquid in the laboratory spinneret, a machine used to remove liquid solvent and leave behind fibers.

In “a case of serendipity,” as she put it, she discovered that polyamide molecules in the solution, a form of liquid crystal, lined up in parallel and that when the liquid was “cold spun,” it produced a fiber of unusual stiffness.

When the fibers were tested in 1965, they were found to be five times as strong as steel of equal weight and resistant to fire. Herbert Blades, Joseph Rivers and others at DuPont soon recognized the market potential for a tough, lightweight fabric and began to consider potential uses for the innovation. They have been credited with making it a mass market product.

DuPont says it spent $500 million to develop Kevlar, what Fortune magazine once called “a miracle in search of a market.” The company initially began developing it for use in tires under the working name “Fiber B” at a pilot plant in Richmond, Va.

Ms. Kwolek later spoke of her uncertainty when testing and retesting the experiment’s findings. “It wasn’t exactly a ‘Eureka!’ moment,” she recalled in 2007.

She added: “I didn’t want to be embarrassed. When I did tell management, they didn’t fool around. They immediately assigned a whole group to work on different aspects” of the fiber’s development.

It took a decade before Kevlar appeared in the form of a vest resistant to bullets fired by handguns. It was made available to police departments in 1975. Later versions increased the layers of Kevlar fabric.

Since the 1990s, the vests have been further reinforced with ceramic plates to withstand rifle fire. Military helmets have been lined with up to 24 layers to make them less vulnerable to penetration by shrapnel.

In 1996, Ms. Kwolek was awarded the National Medal of Technology for her work on synthetic fibers. On Wednesday, the day she died, DuPont announced that the one-millionth vest made with Kevlar technology had been sold.

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She led polymer research at DuPont until she retired in 1986. Information on survivors was not available.

Ms. Kwolek was the recipient of many other honors, including the Lemelson-M.I.T. Lifetime Achievement Award, which recognizes the nation’s most talented inventors and innovators. In 1995, she was inducted into the National Inventors Hall of Fame in North Canton, Ohio. In 2003, she was inducted into the National Women’s Hall of Fame in Seneca Falls, N.Y.

She was also inducted, in 2004, into the Plastics Hall of Fame at the National Plastics Center and Museum in Leominster, Mass. There, her plaque hangs alongside those of innovators like Earl Tupper, the creator of Tupperware.

After retirement, Ms. Kwolek tutored high school students in chemistry, paying particular attention to grooming young women for work in the sciences.

I love that last sentence, where she tutored high school students in chemistry.