Stephanie Kwolek, a pioneering female chemist at DuPont who invented the exceedingly tough fibers widely used in Kevlar body armor, has died, colleagues said Friday. She was 90.

Kwolek died Wednesday at a hospital in Wilmington where she had lived, said her friend Rita Vasta, a chemist who also worked at DuPont. Vasta said Kwolek had been ill about a week though she didn't know the cause of death.

Kwolek made her discovery in the mid-1960s while working on specialty textile fibers, according to DuPont's website. She invented a liquid crystalline solution that could be spun into the exceptionally strong fibers now used worldwide in police and military protective equipment.

In 2007, Kwolek told The (Wilmington) News Journal that the discovery launched an exciting period in her career as the chemical company explored uses for her discovery.

DuPont management "didn't fool around," she told the newspaper at the time. "They immediately assigned a whole group to work on different aspects."

DuPont CEO Ellen Kullman said in a statement that Kwolek was a creative, determined chemist as well as a pioneer for women in science.

"Her synthesis of the first liquid crystal polymer and the invention of DuPont Kevlar highlighted a distinguished career," Kullman said.

Vasta said Kwolek was proud of her work and pleased to learn that even police dogs had been fitted with Kevlar vests.

She also said Kwolek also worked to encourage other women to enter scientific fields once traditionally dominated by men.

"Whenever she had an opportunity to speak to teen girls or little girls, she used all that time to talk about her career in science and say it was important for women to go into science," she said.

U.S. Sen. Chris Coons, D-Del., said in a statement that Kwolek had made the world safer. He called her a legendary scientist and an important part of the history of the small state.

Vasta said a Catholic funeral Mass is scheduled June 28.