Polyester, or Polyethylene Terephthalate (PET) is a plastic material produced by reacting terephthalic acid with ethylene glycol - two substances produced in the crude oil / naptha cracking chain. During manufacture, polyester “chips” are fed into a heated extruder and the molten polyethylene terephthalate (PET) is then extruded onto a chill roll, which quenches it into the amorphous state. It is then biaxially oriented by a process known as drawing. The most common way of doing this is the sequential process, in which the film is first drawn in the machine direction using heated rollers and subsequently drawn in the transverse direction, i.e. at 90° to the direction of travel, in a heated oven. Draw ratios are typically around 3 to 4 in each direction.

Once the drawing process is completed, the film is "heat set" or crystallized under tension in the oven at temperatures typically above 200 °C. The heat setting step prevents the film from shrinking back to its original unstretched shape and locks in the molecular orientation in the film plane. The orientation of the polymer chains is responsible for the high strength and stiffness of biaxially oriented PET film. Another important consequence of the molecular orientation is that it induces the formation of many crystal nuclei. The crystallites that grow rapidly reach the boundary of the neighboring crystallite and remain smaller than the wavelength of visible light. As a result, unfilled biaxially oriented PET film has excellent clarity, despite its semicrystalline structure.