Empervious Shower Pan Extensions are made of a 100% waterproof XPS Foam core, reinforced with fiberglass mesh and finished with a cement coating for added durability. Extensions can be utilized if your shower sizes falls in between a standard pan size. The standard extension works with all center drain pans with sides less than 84". The thick extension is for all offset drain pans and center drain pans with a side 84" or greater.