A method for determining the degree of fusion between flexible vinyl sheets, coated fabrics, and thin sections of cast or molded parts, by immersing the folded specimen in a solvent and observing the elapsed time at which disintegration commences. Useful solvent systems comprise methyl ethyl ketone, tetrahydrofuran, ethyl acetate, and carbon tetrachloride. The preferred solvent system is one that will initiate degradation within 5–10 min in a fully fused specimen. (Handbook of polyvinyl chloride formulating. Wickson EJ (ed). Wiley, New York, 1993).