Teflon frying pan on wooden table

The chemicals once seemed near magical, able to repel water, oil and stains.

By the 1970s, DuPont and 3M had used them to develop Teflon and Scotchgard, and they slipped into an array of everyday products, from gum wrappers to sofas to frying pans to carpets. Known as perfluoroalkyl substances, or PFAS, they were a boon to the military, too, which used them in foam that snuffed out explosive oil and fuel fires.