As the applications of plastic extrusion continue to expand, the requirements for the extrusion solutions become increasingly complicated. Many products designs require multiple functions in a simplified structure. However, each polymer material has its own characteristics and no single of them has the properties that can meet all desired needs. Therefore, the co-extrusion technology is created. Co-extrusion is the process of pressing two or more materials through the same die to produce a single piece, which has opened up new frontiers in material engineering and addressed several previously difficult manufacturing needs.

Co-extrusion involves multiple extruders forming layered or encapsulated parts. Sometimes five or more materials are used in a production line with each extruder delivering the precise amount of molten plastic needed for the operation.

Unlike ordinary plastic mixing, through co-extrusion technology, each individual plastic retains its original properties, but is combined into a compound-material part. If mixed prior to extrusion, the characteristics of the individual materials may be altered, but the end result is a homogeneous product.

Not all plastics are suitable for coextrusion because some polymers will not adhere to others. Plastics with drastically different melting temperatures are also unsuitable for the process, as degradation will occur in the lower melting material. Finally, PVC and acetals should never be coextruded together because of the potentially violent reactions that can occur when they are joined.

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