United States v. E. I. du Pont de Nemours & Co.

du Pont (defendant) held a patent on a moisture-proof cellophane wrapping material and dominated 75 percent of U.S. cellophane production, though it held less than 20 percent of the broader flexible-packaging market (which included products like foil and waxed paper). The United States (plaintiff) sued, claiming du Pont monopolized the cellophane market. du Pont argued the relevant market was flexible packaging generally, since consumers treated other materials as substitutes. The district court agreed with du Pont's broader market definition and found no monopoly. The government appealed.