The award-winning MULTI-SWELL™ 3760-U gasketing material creates a seal where the available compressive load on the gasket is low, or where the flanges are not rigid enough to compress a standard gasket material in the areas between bolts. The seal is created by a combination of highly compressible material and the interaction of the gasket with water or oil that causes the gasket to swell and create load. MULTI-SWELL™ 3760-U is certified NSF-61.