Ask a chemist to name the strongest single bond in organic chemistry, and they'll likely say carbon-fluorine. It's that bond, repeated dozens of times over, that gives per- and polyfluoroalkyl substances (PFAS) their nickname: forever chemicals. Manufacturers prize PFAS for the same reason regulators dread them. The bonds barely break down, which is exactly why the compounds are so good at repelling water, oil and heat in everything from semiconductor fabrication to nonstick cookware. This is also why PFAS persist in soil, water and living tissue long after serving their industrial purpose.