W.L. Gore (plaintiff) sued Garlock (defendant) for infringement of two patents, one claiming a process for stretching Teflon tape under certain conditions and the other claiming products of the Teflon tape stretching process. Teflon tape and certain methods for stretching it were known in the art prior to the Gore patents, though Gore’s inventions were based on the surprising discovery that high speed stretching under certain conditions was possible, while one of skill in the art believed that the most effective manner of stretching tape without damaging it was by reducing the stretch speed. The machine for stretching the tape, known as the 401 machine, was also previously known in the art. Garlock counterclaimed for non-infringement and patent invalidity, the invalidity purportedly based on prior use by another company, Budd. A few years prior to the Gore patents’ filing dates, a New Zealander, Cropper, developed his own Teflon stretching machine. He offered it for sale to a Massachusetts company, though no sale or further disclosure ever occurred. Then, still prior to the Gore filing date, Cropper licensed the machine to Budd, who used the machine secretly to manufacture stretched Teflon tape similar to the new tape made by Gore. Budd and Cropper entered into a confidentiality sales agreement, and Budd further required its employees to sign secrecy agreements with respect to the machine. On the basis of this prior use, the district court held that the Gore patents were anticipated. Gore appealed.