E.I. DuPont de Nemours & Co. v. Yoshida International, Inc.

DuPont (plaintiff) owned the TEFLON trademark for non-stick coatings and sued Yoshida (defendant), maker of an "EFLON" zipper, for infringement; Yoshida defended by arguing TEFLON had become a generic term. Yoshida's surveys asked respondents simply to name the non-stick feature, with over 80% answering "TEFLON" and under 10% naming DuPont as the manufacturer. DuPont's own survey instead asked respondents directly whether a list of terms, including TEFLON, were brand names or common names, with 68% identifying TEFLON as a brand name and 31% as a common name.