Blow Molding

Blow Moulding of Plastics

In general, there are three main types of blow moulding: extrusion blow moulding (hollow plastic parts), injection blow moulding (medicals), and injection stretch blow moulding (PET bottles).

Blow moulding is a specific manufacturing process by which hollow plastic parts are formed and can be joined together.

The process principle started from the idea of glassblowing. Enoch Ferngren and William Kopitke produced a blow moulding machine in 1938.


Process Steps

  • Melting down the plastic and forming it into a tube-like piece of plastic, through which compressed air can pass.
  • The tube is then clamped into a mould and compressed air is blown into it.
  • The air pressure then pushes the plastic out to match the mould.
  • Once the plastic has cooled and hardened the mould can be opened.


  • New form of technology to produce hollow objects.
  • Tooling is less expensive than in injection moulding.
  • No loss of plastic material.



  • The cost of blow moulded parts and the equipment are higher than in injection moulding.
  • Not possible to mould in holes except after the moulding.
  • it is less accurate regarding wall thickness.


Examples of applications

Blow molding is more specialized for hollow objects, although it is less accurate regarding wall thickness with this dimension being an undefined feature (unlike in an injection mold where all dimensions are predetermined).