A friend, Rita Vasta, said Kwolek had a brief illness.
DuPont plans to mark Kevlar's 50th anniversary next year. Kevlar is best known for its use in body armor and other protective equipment for police and the military; it is also used in athletic equipment and other items where its combination of strength -- 50 times that of steel -- and flexibility are useful.
"We are all saddened at the passing of DuPont scientist Stephanie Kwolek, a creative and determined chemist and a true pioneer for women in science," DuPont CEO Ellen Kullman said in a statement Thursday. "Her synthesis of the first liquid crystal polymer and the invention of DuPont Kevlar highlighted a distinguished career."
Kwolek discovered the polymer in the mid-1960s. She said later that she only made the initial discovery and other scientists helped develop Kevlar as part of the DuPont team.
"They immediately assigned a whole group to work on different aspects," she told the Wilmington News-Journal in 2007. "It was very exciting, let me tell you."
Kwolek spent her entire career at DuPont. She was hired in 1946 -- an opportunity she may have received because many men were still in the military in the months after World War II ended -- and retired 40 years later.
Vasta said Kwolek was her mentor when she joined DuPont in the 1980s and helped many other women.
The Kevlar Survivors' Club, a partnership between DuPont and the International Association of Chiefs of Police, says it has found at least 3,200 people whose lives were saved by Kevlar. Ron McBride, a former police chief in Ashland, Ky., and former manager of the club, said one of them was his son, who served in Iraq.
"When you think about what she has done, it's incredible. There's literally thousands and thousands of people alive because of her," McBride said. "She could look back on her life and say, 'Yeah, I made a difference.'"