In determining illegal antitrust conduct, the definition of the relevant product market has been very import. For example, in the well-known cellophane case, Dupont was accused of monopolizing the market for cellophane. In its defense, Dupont argued that cellophane was just one of many flexible packing materials that included cellophane, waxed paper, aluminum foil, and many other. Based on the high cross-price elasticity of demand between cellophane and these other products, Dupont successfully argued that the relevant market was not cellophane but flexible packaging materials. Since Dupont had less than 20 percent of this market, the Supreme Court ruled in 1953 that Dupont had not monopolized the market. The most celebrated antitrust case of the 1990s was the one against Microsoft (see Case Study 12-6)