Yes, exactly that stuff...it is a flexible pvc liner you put down, fold corners (like military bed corners) and seal with special pvc cement before you pour the shower floor and set tile. Better than pond liner rubber because it is made specifically to resist the effects of concrete (both chemical and from grit, gravel, etc). It is very tough stuff but still has flexibility and "give." As an anti-squeak it is pretty much the best you can use in my opinion. Much better than the tar paper junk some sell because it won't harbor moisture.
