You know how it is: Wear your favorite pair of jeans over and over and after a few days, they’re hanging loose. Do the same with a pair of yoga pants or cycling shorts, though, and they’ll remain just as stretchy and form-fitting as the first time you put them on. We’re not suggesting you try this at home (unless you want to be known as the smelly roommate), we’re just giving a nod to one of the greatest inventions in the history of fitness: spandex. And we have Joseph Shivers, PhD, a curious and perhaps stubborn chemist at DuPont, to thank.

During his time at DuPont, Shivers set out to find an alternative to rubber, which, in addition to being the primary material used to make tires, hockey pucks, and shoe soles, was also used for women’s girdles (yikes). It’s no surprise this wasn’t the ideal textile for clothing; rubber doesn’t breathe, which made the body-hugging garments extremely uncomfortable. Plus, rubber was in high demand and short supply during World War II: Its use in consumer products was curtailed and the material was diverted to the military to support the war effort. The resulting shortage of rubber added to the demand for an alternative material. (If tires were being rationed, things probably didn’t look so good for ladies’ shaping undergarments.) So in 1949, Shivers and his colleagues developed a new elastic fiber. Tests revealed that when spun into a form-fitting fabric, the fibers expanded, allowing plenty of give (great!) but wouldn’t contract like rubber, which meant wearers of these new girdles would find bulges in their midsection when they went from sitting to standing (not so great).

The search for a rubber alternative was tabled shortly thereafter, but Shivers remained curious. Five years later, he developed a new kind of fiber that could be stretched up to five times its original size without losing its elasticity. The one problem: Spandex (marketed by DuPont as Lycra) hit shelves just as girdles were going out of fashion in favor of pantyhose. Spandex proved versatile, however, and soon found its way into swimwear and then runner’s leggings with the rise of jogging in the 1970s, before it ended up in our beloved Lululemon yoga pants in the late 1990s. But spandex hasn’t strayed too far from its organ-squeezing roots: Spanx, the shapewear du jour, is made of Lycra and polyester.

So here’s to you, Joseph Shivers. Thanks for playing a major role in making it totally acceptable to basically wear pajamas in public.