Injection blow moulding (IBM) is a process of shaping plastics (and sometimes glass) into a predetermined shape. Mostly, these are hollow shapes that form containers such as bottles and buckets. It is one of three known blowing processes. Others include injection stretch and extrusion blow moulding.

The process is used to produce these containers on a massive scale. It is divided into three distinct parts:

  • Injection


  • Blowing


  • Ejection



The first part here is melting of the polymer which is done using the extruder barrel. The plastic granules are exposed to high temperatures that turn it into a viscous liquid. The liquid is then pushed under pressure (injected) through nozzles into a preformed mold which has the shape of the required container.

The preform mould remains on the exterior of the molten polymer while a core rod known as a mandrel restricts it from inside.


With the plastic having assumed the shape of the mould, compressed air is blown over it under high pressure to cool and solidify it. The exterior mould is opened up and the main task falls to the core rod.

The rod rotates and clamps onto the blow mould then allows the pressurized air to inflate it into the final shape of the container. The shape is then allowed to cool before the process proceeds to its final step.


Once the moulded container is complately solid and firm, the blow mould is opened to release it. The core rod unclamps and rotates backward until it reaches an ejection position. From this position, both the mould and the core rod are withdrawn and the new form is left as a stand-alone container.

As innovations in injection blow moulding continue, new types of core rods have been created that allow all three processes- injection, blowing and ejection- to run concurrently in a seamless manner.

Injection still remains the least used blow moulding technique in the production of plastic containers.

23,766 thoughts on “Understanding the Injection Blow Moulding Process”