170.5 Sound & Crack Isolation Mat is a high-performance acoustical underlayment system that muffles impact noises through ceramic tiles, stone, and other hard surfacing materials. It also minimizes the transmission of cracks from the substrate to the tile installation up to 1/8" (3 mm) non-movement cracks. 170 Sound & Crack Isolation Mat is a 5 mm thick rubberized membrane comprised of 88.5% post-consumer recycled materials.