Chemist Stephanie L. Kowlek, who is credited with developing Kevlar, died this week at a hospice in Wilmington, Delaware, a friend told the Washington Post. She was 90.

Rita Vasta, a former colleague at DuPont, declined to reveal the cause of death.

Kwolek discovered Kevlar, the fiber used to make bullet-proof vests and helmets, after being assigned the task of developing a material that could be used to reinforce automobile tires. The material also is used to strengthen boats, planes and sports equipment and is woven into protective garments and ropes.

“Not in a thousand years did I think the discovery of this liquid solution would save thousands of lives,” she said in a 2003 interview with USA Today. “When I watch the war on TV, I take great pride in saying, ‘We at DuPont invented that.’”

Kwolek was born in 1923 in New Kensington, Pennsylvania, to Polish immigrant parents. She attributed her interest in science to her father, John, who was a naturalist. She was hired at DuPont's Buffalo, New York, facility in 1946, ending plans for a medical career.

Kwolek retired in 1986 but continued to serve as a consultant for DuPont and served on the National Research Council and the National Academy of Sciences. She also was named to the National Inventors Hall of Fame and won the 1997 Perkin Medal from the American Chemical Society and the 1980 award from the ACS for creative invention.