The protective film on the aluminium plate is made of PE thin film. Specifically, the film is co-extruded by three layers of thin film. The film can be sticked to the aluminium plate to protect the surface of the aluminium plate from unexpected scratches and damage after it's covered with glue.
If you want to learn more about PE protective film, you can go to the PP forum. There are many insiders who are specialized in this field.
