Co-extrusion is the production of a multi-layer film in a single pass by combining the melts from more than one extruder in layers in the same die. Because each layer is fed by its own extruder, it can contain different raw materials or additives.
This method makes it possible to combine different functions in a single film. For example, the outer layer can offer a surface suitable for printing while the middle layer provides strength and the inner layer is chosen to seal well. Recycled material is also often used in the middle layer. The number of layers depends on the type of line; more layers allow a finer division of functions between layers, but also make the line and its settings more complex.