Stephanie L. Kwolek, the DuPont chemist primarily credited with the invention of Kevlar, died today at the age of 90. Nearly fifty years ago, in 1965, she created a cloudy liquid polymer solution that seemed to be a disappointment at first. When spun into a fiber, however, the resulting material was incredibly strong and lightweight — pound for pound, it was five times stronger than steel. And it was fire resistant, to boot. Her discovery ultimately led to Kevlar fabric, though DuPont spent 15 years and $500 million developing the product and finding uses for the life-saving material.

Today, Kevlar is best known for its use in protective body armor and helmets worn by police officers and the military. DuPont estimates that the material has protected over 3,000 police officers from serious gunshot wounds. But the material created by Kwolek wasn't designed to stop bullets. Kwolek and other DuPont chemists in the mid-1960s were seeking to create a lightweight replacement for the steel used to reinforce tires. Kevlar has gone far beyond that original goal: it's now used in everything from sails and butcher's gloves to mattresses and fiber optic cables.