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Injection Molding vs Blow Molding: What’s the Difference?

There are two distinct processes, injection molding vs blow molding, that play important roles in the custom manufacturing of disposable and reusable plastic components used in the biomedical, research, and medical diagnostic fields worldwide.

Injection Molding vs Blow Molding What's the Difference - KB Delta

Injection molding vs blow molding are two unique processes that have crucial roles in custom manufacturing disposable and reusable plastic components used worldwide in the biomedical and research fields and in medical diagnostic laboratories. In addition, these processes are two of the most popular methods for producing cost-effective, high-quality plastic components.

This article highlights the significant differences between injection molding vs blow molding, starting with what each process is.


What is Injection Molding?

Injection molding requires extraordinarily upfront engineering to develop extensive molds or tooling. First, molds are usually crafted from aluminum or stainless steel. Next, they are injected with liquid polymers at high temperatures under extreme pressure. Finally, the molds are cooled to release complete plastic components.


Advantages of Plastic Injection Molding

Injection molding has several advantages, making it one of the most utilized plastic-making processes. Some of these advantages include the following:


  • Efficient use of materials, as well as low scrap rates
  • Highly engineering and detailed tooling with multi-cavity mold options
  • Efficient and precise processing for large volumes of small components
  • Flexibility in being able to change the color or type of material that is being used


Injection molding is a unique process appropriate for mass production and high-volume orders in projects requiring thousands or even millions of the same component. They must have an incredibly high precision match between mold halves. This ensures material flow is utterly controlled.

Creating the mold is crucial in plastic injection molding as it helps build an ideal precision component. As soon as the production mold is nailed down, manufacturing begins right after the machine is prepped.

Quality checks take place from time to time, depending considerably on the component being produced and the agreement with the molder. An initial run will undergo a thorough examination for any component defects. If no defects are found, the full production of plastic components begins.

The molder inspects for color correctness, strength, and any other common defects that may occur, like warping or flash. The precision of injection molds makes them much more expensive than blow molds.


What is Blow Molding?

On the other hand, blow molding follows a process akin to the basic steps associated with glass blowing. The entire blow molding process is primarily designed for manufacturing high-volume, one-piece hollow items or objects.

For instance, blow molding is the process to go for if you need to create lots of bottles. Blow molding creates uniform, thin-walled containers economically.


Advantages of Blow Molding

Blow molding has several distinct advantages:


  • The costs of machinery are typically lower compared to injection molding
  • The costs in blow molding are generally lower as well
  • This process is a one-piece construction that does not require the connection of part halves, which can accomplish shapes that is impossible to produce using injection molding.


When it comes to blow molding, a plastic tube is heated and then filled with air until it becomes a ‘parison,’ i.e., a balloon of hot plastic. Next, the operator clamps a mold around the parison, efficiently trapping the plastic. At the same time, air continues filling the balloon with hot plastic, transforming it into the shape of the desired component.

The size of the blow mold equipment and the related costs required for producing a blow mold product is based primarily on the weight of the plastic shot employed in the mold.

Molds are generally water-cooled to regulate their temperature and speed up solidification efficiently. As soon as the plastic solidifies and becomes firm, the mold opens, and the flash is swiftly trimmed away from top to bottom.

Blow molds offer more design freedom, especially between mold halves, because every mold half creates its wall shape. Creating the mold is highly essential in blow molding; however, a few variables require monitoring, such as:


  • Air leaks
  • Streaks
  • Wall thinning
  • Flash


For instance, the wall thickness variation is a vital factor that product designers must consider. Quality control is also a critical aspect of the entire process. This is why you must look for a qualified supplier trained and capable of measuring, monitoring, and improving each aspect of the product. This should be easy since more than 500,000 suppliers are out there. Finding one that matches your requirements or exact needs should be relatively easy.


Product Examples

A few examples of products formed using blow molding include:


  • Reciprocating compressor components
  • Water bottles
  • Stadium chairs and seating
  • Shampoo, as well as other small bottles
  • Coolers
  • Watering cans
  • Any other type of hollow components or products


Co-extrusion and stretch blow molding are highly specialized variations of the traditional blow molding process. They are mainly employed for making clear bottles.


Injection Molding vs. Blow Molding: The Differences

According to the descriptions above, injection molding and blow molding are unique processes for creating plastic-based items. However, this is where their similarities lie.

Injection molding and blow molding have a few considerable differences. Here are they, highlighted in no particular order:



Injection-molded products or shapes are pretty solid, except when complex cores are utilized. But shapes produced via blow molding are usually hollow.



Blow molding and injection molding equipment are complex and extensive. However, injection molding machines are costlier due to the forces involved.


Variation of wall thickness

Injection molding has higher uniformity and precision than blow molding.



Blow molding tools are less massive than injection molding tools. However, the latter’s tools must be heavy and solid enough to withstand the incredibly high clamping pressures required to prevent the two halves from separating under the injection force.


Tooling costs

Blow molding tools are cheaper or less expensive than injection molding.


Material consumption

Blow molding is generally capable of creating thin plastic walls. This shows that the containers produced using blow molding are lighter and require less material – significantly reducing transportation costs – than those created using injection molding.



Injection and blow molding are two of the most popular processes for creating plastic-based products. Although they sound similar, they function uniquely and produce different plastic components.

Knowing the significant differences between injection molding and blow molding is essential. It helps you decide which processes suit your needs or requirements. You also know which processes are cost-effective in terms of maintenance, production, and ease of operation.



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