Bi-axially drawn PET films have many superior properties to non-oriented films, such as their mechanical properties, barrier functionality, and better profile. This can be explained by the orientation process, which is performed when a polymer is stretched above the glass transition temperature. After the drawing in Machine Direction (MDO), most of the polymer chains are oriented in Machine Direction (MD). After the drawing in Transverse Direction (TDO), they are mainly oriented in the plane of the PET film.
