Abstract: A machine and method for detecting and identifying the approximate location of air leak-causing defects in flat, thin rubber stock used to manufacture inflatable, expandable bags. The detection of air leak-causing defects is accomplished by continuously moving at a relatively constant rate the flat rubber stock to be tested between two cylindrical rollers. These two rollers are maintained at a voltage which will fluctuate in response to any air leak-causing defect passing between them. The machine disclosed is composed of a frame to which is mounted a feed spool and a take-up spool, numerous supports and guides, a set of two test rollers, a dielectric analyzer, and a marker which punches the edge of the rubber stock adjacent to the in-line location of a detected defect. The disclosed machine and method enable detection of small pin-hole sized defects often undetectable to the naked eye.