Flex Seal - Liquid Rubber Sealer in a Can! Stop leaks fast! The easy way to coat, seal and protect! Flex Seal sprays out a liquid, seeps into cracks and holes, and dries to a watertight, flexible rubberized coating! Excellent roof patch. Fills cracks and voids. Flexible, watertight coating. Can be used on wet surfaces too. Unaffected by weather and seals out the elements.