What is the Difference Between Injection Molding and Blow Molding?

Injection molding machine internal structure
Injection molding machine internal structure
Resource: https://www.researchgate.net

Although often confused, the difference between injection molding and blow molding is seen in many stages of the processes. Understanding these differences is, therefore, critical when deciding what method to use. If that’s what you’re looking for, this comparison article is for you; we’ll not only compare the two, but will also provide important advice on when to use either technique.

What is Injection Molding?

Injection molding means the part-making method where a raw material—usually a type of plastic—is heated in a barrel before being forced into a preformed mold under intense pressure. The melt is then, using a controlled cooling process, allowed to harden before being removed from the mold.

Injection molding is typically employed in manufacturing facilities to make solid or thick walled items, either for industrial processes or end user purposes. Depending on the injection molding mold design, these can be parts for automotive and medical industries or parts for consumer products such as electronic appliances.

Blow molding mold
Blow molding mold
Resource: https://www.youtube.com/watch?v=j05NS0Dhmps

What is Blow Molding?

Blow molding, on the other hand, is defined as the process where resin is melted and then molded into a product using a blast of compressed air. The air serves to expand the viscous plastic or preform, causing it to spread around the walls and profile of a mold.

As the blown material cools, it hardens in the shape of the particular mold. This produces a hollow product with thin walls. Blow molding product manufacturers use this process to make a range of plastic containers: packaging bottles and jars, appliance components, and more.

With these definitions, let’s now dive right into the injection molding and blow molding difference. This will help you understand how these two plastic molding methods are different or similar, and how each process suits (or does not suit) your project.

Injection molding mold
Injection molding mold
Resource: https://youtu.be/XqoecH2AtaQ

Difference Between Injection Molding and Blow Molding

The difference between injection molding and blow molding makes each process unique and suited for different manufacturing requirements. It also means variation in these areas; type of machine to use, mold design and cost, best materials for each molding method, and overall costs. These aspects are discussed below.


The first injection and blow molding difference we’ll look at is the type of machine used—its construction and working. This is because different parts and stages are involved, and each stage introduces or requires a unique process.

In the injection molding machine, immense pressure is needed to drive plastic melt into the channels leading to the mold and the mold itself. That requires a more detailed construction and strong mold. This is in contrast to the less detailed construction of the blow molding machinery.

Depending on the blow molding technique, the machine may use two sets of molds, one for the preform and another for the final product. It also requires a source of compressed air, unlike when using the injection machine.


Another difference between injection molding and blow molding is seen in the design of the mold and its cost. Starting with the injection mold, we can see that it has to withstand extreme pressures and is, therefore, normally a robust one made from aluminum or steel.

Injection molding mold types assume a similar construction, and only the profiles changes to fit the product design requirements. Blow molding molds are different for the different types of the process, which include stretch and extrusion techniques.

In terms of cost, injection molds are more expensive, seeing that they are a more complex design. In most cases, the injection molding mold cost starts from $10 000. This is compared to the tooling cost of blow molding, which can be as low as $1000.


Injection molding parts are usually solid or thick-walled, while blow molded parts are mostly hollow and with thinner walls. That means your parts will be different for each method, and your application should dictate whether to use injection or blow molding.

If you intend to make thick walled parts, then blow molding may not be the right choice for your project. However, you get more product design options when using blow molding. This is something you might want to consider if looking for a unique article, plus the tooling costs are comparatively low.

It’s also worth noting that injection molded parts will normally require post processing operations. Blow molded products, owing to the type of process used to make them (blowing the material into a parison), often do not require post-processing.


The two techniques, injection and blow molding, utilize different materials depending on the intended use of the product and other reasons such as material suitability for the specific method. Here’s how they compare in terms of available options:

Injection molding materials are more varied and include thermoplastics and thermosets. The material can even be metal powder that has been infused with polymer for a more solid and durable part for demanding applications.

On the other hand, the range of blow molding materials is small and includes thermoplastics and thermoplastic elastomers. These are materials that can be blow molded, using air, to produce hollow containers and other parts.


Comparing the blow molding vs. injection molding cost, we can see that blow molding is a cheaper alternative. Less material is used and the process doesn’t require pressure or much energy. That being said, injection molding is capable of higher production speeds, which results in lower costs per part in the longer run.

With injection molding, you can produce robust products that are versatile enough for a variety of applications. On the other hand, blow molding can only produce products with thin walls. These mostly find use in the packaging industry, although other different applications are also possible.


Now that you know the difference between injection molding and blow molding, you can go ahead and select the method that best fits your particular project for the discussed parameters. These include part design, intended use, and other aspects such as strength and cost. That’s because each process has its advantages or best applications, and your choice will depend on them.

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