At least one inventor of a famous machinegun has spiritually grappled with having invented a tool for killing. But Stephanie Kwolek, a scientist for DuPont who passed away last week at the age of 90, accidentally invented something that protected people from firearms: Kevlar.

Carnegie Mellon grad and chemist Kwolek was a female pioneer in the sciences. She began working at DuPont in 1946, an era when women were expected to be housewives. By the 1960s she was trying to develop an ultra-strong fiber that could be incorporated into radial tires, and created a polymer that, in liquid form, at first appeared to be disappointing.

But she persevered and had her concoction run through a lab spinneret, which turns liquids into fibers. To her and her team's surprise, when the resultant fibers were exposed to stress tests, they would not break at the point that more common nylon would. Further investigation revealed that what Kwolek had created was five times stronger than steel.

When she brought the report to management, "they didn't fool around," Kwolek said in a 2007 interview. "They immediately assigned a whole group to work on different aspects."

DuPont knew they had a materials hit on their hands and threw a reported $500 million in development money at it over the years. And while the resultant material, Kevlar, did make its way into the tires it was originally targeting, by the '70s it had found its lifesaving application as the key component of bulletproof vests.

Kwolek, who put in 40 years of service at DuPont and retired in 1986, racked up a host of accolades: She garnered both the Lemelson-M.I.T. Lifetime Achievement Award and the National Medal of Technology, and was inducted into the National Inventors Hall of Fame, the National Women's Hall of Fame and the Plastics Hall of Fame at the National Plastics Center and Museum.

But for every medal she was able to place around her neck, there were and are countless men and women around the world who can strap on vests woven with the fiber she created. A local newspaper reporting on Kwolek's passing puts this in perspective:

"When you think about what she has done, it's incredible. There's literally thousands and thousands of people alive because of her," said Ron McBride, former manager of the Kevlar Survivors' Club, a not-for-profit partnership between DuPont and the International Association of Chiefs of Police. The group has documented 3,200 lives saved through use of Kevlar in body armor.

McBride is a former chief of police in Ashland, Kentucky. A vest with Kevlar saved the life of his son, who was serving as a naval operative in Iraq.

"She could look back on her life and say, 'Yeah, I made a difference,'" he said.

Kwolek passed away at the age of 90.

For those interested in learning more, here's a video Called "Stephanie Kwolek - Curiosity and the Discover of Kevlar," put together as part of the Chemical Heritage Foundation's "Women in Chemistry" series: