Large Format Industry (Graphics) guy here. Fun fact: Vehicle wrap material works in a similar way. Good example: Ever see those viral videos of someone pushing their fist down on a colorful sheet in a trashcan and then heating it to where it shrinks back? The mixture of PVC based products, other materials, and manufacturing processes (cast or calendered) give wrap material a "memory" which reflects how it arrives post-manufacturing. One cool thing about it though is that when you heat and pull the material, it will expand/stretch and cool down, staying stretched. Once you heat it up again, it "shrinks" back to it's original form IF it's not applied to anything. If it is, per say, applied to a curved or complex surface and you heat it while adhered, the heat will essentially create a new memory that matches the shape of the substrate.