What is Co-Extrusion?

Co-Extrusion

Co-extrusion is a process that allows two, or more, melt streams to combine in a die to 

make an extrudate from two or more materials. This process is now linked to 

thermoplastics materials, although it was first used with rubbery polymers to make an 

extrudate with layers of different colors. With thermoplastics, the layers of material are 

often combined in the die.

The simplest example combines only two layers, for instance a colored layer on a natural 

core, which saves on colorant costs. Films based on three or more layers are common in 

the packaging industry. Laminating two or more different polymer layers together can 

result in a product that has better barrier properties than those obtained when only a 

single polymer is used.

One of the polymers frequently used is a moisture or gas barrier layer based on polyvinyl 

alcohol (PVAL). Usually, two or three extruders are used to produce three-layered structures. 

In the blow-molding process, co-extrusion and bi-axial orientation can possibly be combined 

to produce lightweight yet strong bottles that extend the storage life of products.

Layered co-extrusion is not the only form of co-extrusion. A sequential co-extrudate can be 

produced by combining the materials one after the other. This may include a hard thermoplastic 

material combined with a soft thermoplastic material. Alternatively, two materials can be 

extruded side-by-side, for example, a clear material together with an opaque material, to 

produce a sheet for making thermoformed trays.