Blow-moulding technology is based on air blowing into a plastic tube of 0.5 to 2 mm wall thickness (in order to enlarge its size by 2 to 5 times) which is drawn through a take off device (to achieve up to 5-fold elongation). The blown film, usually with a wall thickness of 0.015 to 0.3 mm, is then cooled and wound up. LDPE, HDPE, PP, PVC, PA and PET films are made by blow moulding. Multi-layer films with various compositions of material are also produced by blow-moulding. Such films can have up to seven layers. The design of extrusion heads for multi-layer films is very complicated and their use in producing film requires strict compliance with the production procedure.