Whenever possible you should purchase a piece of shower liner from a roll which all
the Home and Garden stores stock. However; if you do get a piece that has a crease in it, lay it on a flat surface in the sun or heat with a hair dryer. Then lay a flat heavy object on top of the crease for 30 minutes. This step may have to be repeated a few times in order to create new material memory. If the creases are too large, DO NOT install the liner. Large creases left in the liner will cause water to puddle under the concrete which could affect the integrity of the cement base, or mold growth which will transfer up through the grout joints. The pan liner must be self-draining.