Guru's G-Flex Uncoupling Membrane is a waterproof and crack isolation membrane made of High-Density Polyethylene (HDPE) that is 1/8" thick. It is designed to protect and improve the durability of tile installations both outdoors and indoors, while also providing an anti-fracture waterproof surface. Get 323 sq ft of coverage (3'3" x 98'5") or 150 sq ft of coverage (3'3" x 45'9"), and make sure your tile projects are done right to protect your investment.