Polypropylene film. Polarised light micrograph of a polypropylene (a type of plastic) film. From close up it can be seen that the film is a symmetrical pattern of hollow triangles. This structure is important when the film is used in sticking (adhesive) plasters. The hollow triangles allow air to circulate around the wound, assisting healing. Polypropylene is a thermoplastic polymer, that means that when it is heated, it will become soft and mouldable. This makes it ideal for articles such as films. Magnification: x12 at 35mm size.