Description Flex Tape is a super strong, rubberized, waterproof tape that can patch, bond, seal and repair virtually anything. It is specially formulated with a thick, flexible, rubberized backing that conforms to any shape or object. This durable adhesive tape instantly seals out water, air and moisture to create a super strong, flexible, watertight barrier. Unlike other tapes available, Flex Tapeâs bond will increase with time and pressure.