What is the difference between Blow Moulding and Injection Moulding?

If you’ve been involved with plastic bottle production in South Africa or abroad, you’ve probably come across the term ‘blow moulding’ or ‘injection moulding’. Chances are, you’ve come across both and wondered to yourself “what’s the difference?”

While you can essentially use both to produce a plastic product, the process is very different, and oftentimes you will want to choose one process or the other for creating the product you want efficiently and effectively.

This blog post will explain the differences between blow moulding and injection moulding, and briefly highlight the advantages of each one. It will also suggest which of the two methods will be best depending on your own product and expectations.


Blow Moulding

Blow moulding is a process that dates back hundreds of years, and was the process first used to create glass bottles. It is designed to create high volume, one-piece hollow objects – think simple plastic bottles and containers. The process can create very uniformly, thin-walled containers and it can do it at a very economical rate.

The Process

With blow molding, a plastic tube is heated and filled with air until it essentially becomes a balloon of hot plastic called a “parison.” A mold is then clamped around this, trapping the plastic while air continues to fill the parison into the desired shape, dictated by the mould used.

The size of the machine and associated costs to produce a blow molded product is based on the weight of the plastic used to fill the mould.

The Product

Blow moulded products often have more design freedom because each mould half forms its own wall shape. However, it is important to choose the right producer when using blow moulding because variables such as wall thinning, air leaks, flash and streaks could create defects. Thus, quality control is an important part of the process, and the supplier must be qualified and trained to measure, monitor and improve the product as it is running in the factory.

Unique Advantages

  • The costs in blow molding are lower as compared to injection molding
  • Machinery costs are typically lower
  • One-piece construction – it can achieve shapes that injection molding cannot produce 


Injection Moulding

Injection moulding relies on a great deal of upfront engineering to develop detailed moulds. The process is designed for high-volume orders for projects that demand thousands or even millions of the same part. Items such as plastic bottle caps, small yet sturdy containers and machine parts are usually the domain of injection moulding.

The Process

In a nutshell, moulds are injected with liquid polymers at high temperatures under extreme pressure. The moulds are then cooled to release complete plastic parts. It is essential that each mould half has a high precision between the two, so that material flow is perfectly controlled. The most important part of injection moulding is creating the mould itself – once it is finalised, manufacturing can begin en-mass.

The Product

Unlike blow moulding, injection moulding has to have exact precision when aligning the two mould halves, which means that injection moulding does not offer the same design freedom as blow moulding. However, injection moulding is perfect for the mass production of singular plastic parts, and the product itself often provides no problems once the mould is finalised.


Unique Advantages

  • Detailed, highly engineered tooling with multi-cavity mold options
  • Precise, efficient processing for large volumes of small parts
  • Efficient material use and low scrap rates


What B&I Offers You

Here at B&I Polycontainers, we can offer you the best of both worlds.

As a proudly South African packaging producer, we run and operate both injection moulding and blow moulding for our customers, and we have a great business relationship with top-tier plastic moulding and tooling creators. 

If you would like to find out more about injection or blow moulding, or are looking for a supplier who can create the bottle of your dreams, contact B&I Polycontainers today.


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