Kerdi-Board Building Panels by Schluter
Imagine a type of waterproof foam panel strong enough to form a partition wall yet soft enough to be trimmed with a box knife and assembled with adhesive. Oh, wait—got it: With these panels you can build the most intricate of bath structures, like a shower bench, and tile directly onto them. No more framing and sheathing in backer board.
About $2.60 per square foot; schluterkerdiboard.com