Blow Molding vs. Injection Molding for Plastic Manufacturing

Table of Contents

Injection Moulding

Blow molding and injection molding are two very prominent processes employed in plastic manufacturing, and a blow molding vs. injection molding comparison occurs frequently. 

Both methods dating back to primordial manufacturing times provide manufacturers with the option to produce both simple and complex plastic products. Products that will, in turn, offer alternatives for numerous industries that utilize plastic materials and components in their respective fields. From daily disposables to intricate components seen in automotive and aerospace tools.

But while blow molding is synonymous with making hollow parts, injection molding focuses on more intricate, precise, and efficient elements. 

Let’s find out how beneficial both methods are to plastic production, alongside their similarities and differences. 

Plastic bottles before processing
Plastic before processing with a blow molding machine

1. Understanding Blow Molding

1.1 Process Overview

The blow molding process is a technique similar to the ancient glass-blowing style. Its specialty is creating hollow plastic parts such as containers and disposable bottles typically used in packaging our everyday consumables. The blow molding process consists of meticulously organized processes that start by loading the feed barrel with plastic granules. These granules are melted in the feed barrel and form a molten tube plastic commonly referred to as the parison. 

At this point, a water-cooled mold collects the parison formed. It transfers it to the next phase, where pressurized air is blown into the parison allowing it to take the form of the mold, and this results in the desired shape being produced. On top of that, the molded part is cooled off, and the structural integrity is assessed by allowing airflow into the molded parts. Once the airflow can’t escape, the molded part is fit for use. 

However, a leak means the plastic is reintroduced into the closed-loop system. Furthermore, excesses removed from the plastics are likewise recycled into the plastic production process. 

Two types of blow molding exist. First is the extrusion already discussed and intrusion blow molding. This entails a preformed plastic by injection molding that is transferred to the blow mold, which takes the desired shape, then cools. 

1.2 Advantages and Limitations of Blow Molding

Blow molding features many advantages for several applications and industries, and these benefits are highlighted here. 

Firstly, its carefully organized steps allow for mass production. Moreso, its cost-effectiveness presents manufacturers with a double bargain of output. Blow molding is efficient for the large-scale production of identical plastic products with the same dimensions and sizes. 

A more significant benefit is the production of lightweight parts, which lessens the cost of material used, including handling and transportation. What’s more, the pressure employed in blow molding is less than the pressure utilized in injection molding, this translates to reduced tooling cost, and that right there is a bonus every manufacturer will opt for. However, high-quality mold manufacturing is still a primary requirement for this molding process. 

Despite these significant contributions to plastic manufacturing, blow molding still has certain limitations, also presented here. One such is its inability to make thick-walled parts. This limits its application to industries that use thin-walled plastic parts, like the packaging industry. In addition, blow molding has lower design flexibility – a critical criterion in the high-quality mold manufacturing industry

It can sometimes be too complex, significantly increasing its setup costs. It also requires post-molding processes to remove the excesses from the head and tail, unlike injection molding, which requires no further post-molding processes.

Industrial Injection molding machine
Industrial Injection molding machine

2. Exploring Injection Molding

2.1 Process Overview

As a manufacturer of plastic parts, if what you desire is an efficient, fast, and precise production, then injection molding is your best bet. This method of plastic part production delivers speed and accuracy. It also involves fewer steps to arrive at the final component. Injection molding entails heating plastic pellets in a barrel at a high temperature. 

Once you have a molten plastic material, it is forced into the mold with an increased pressure that pushes the melted plastic into the mold. What comes next is the cooling process, where the temperature is systematically reduced for the material in the molds. Let’s not forget that the mold already has the desired design the plastic is to take. 

Consequently, the final product is ejected from the mold once cooling is completed. Most times, the material melted in injection molding is thermoplastics. This material adequately provides the necessary properties required for injection molding. Injection molding is suited for rapid plastic production and can fabricate intricate designs. 

2.2 Advantages and Limitations of Injection Molding

It is understandable for manufacturers of plastic parts to opt for the injection molding method. But here’s why. Primarily, the steps employed in injection molding are shorter, can handle complex designs, and complete production in a quicker turnaround time. 

Expectedly, these benefits come at a cost, but most manufacturers won’t be troubled, provided it serves their project needs. Thus, injection molding is quite beneficial compared to other molding methods, allowing design flexibility, unlimited application, repeatability, and accommodating a range of thermoplastic materials and blends. 

In all its glory, injection molding still has a few drawbacks. Probably the most crucial disadvantage is the initial cost of setting up. The molds used in injection molding are specific and precisely designed. Equally, injection molding may take a little longer for the part to solidify and cool off. Furthermore, because of the high-pressure injection molding, the molds can be subject to wear, which may impact production. And unlike the blow molding method, the only design constraint of injection molding is its inability to make hollow designs. 

Despite all limitations, injection molding justifies its hype in precision, quality, and versatility.

3. Comparing Blow Molding and Injection Molding

3.1 Process Differences and Similarities

At this point, we believe the primary differences between blow molding and injection molding methods, especially with their processes, are apparent. However, a deeper comparison is necessary to understand these differences fully. While the blow method is used for creating hollow plastic parts, injection molding, on the other hand, is unable to develop such parts. In addition, each process offers distinctive styles of making the desired shapes. 

Blow molding is capable of two separate ways of achieving the same goals. One is by extrusion, where molten plastic is extruded via the machine head and is then enclosed in a water-cooled mold. The other is by retaining a preformed injected plastic form in the mold for the air pressure inserted to blend it with the mold. Then cooling and solidification takes place to complete the process. 

Meanwhile, injection molding completes its process by injecting melted plastic directly into the mold, which already has the pre-designed shape, then cooling and solidification complete the process before ejecting it.

Some noteworthy similarities are in the range of materials. Both methods accommodate the use of thermoplastics and their blends in their production. Moreover, both processes can make complex designs and dimensions. This equals versatility, quality, and precision for both methods.

3.2 Cost Considerations

Regarding cost considerations with both methods, injection molding costs of tooling are high. However, this can be no issue in faster production cycles. This allows the production of multiple parts in a short time frame. The increase in the tooling cost of injection molding is due to the custom-made molds made to specific designs. 

With blow molding, tooling costs are not as high as in injection molding. Moreover, the ability of the blow method to recycle waste materials reduces the production cost. Nonetheless, the production cost will likely increase when manufacturing higher volumes of plastic parts using the blow method. 

3.3 Design Flexibility

If you’ve been paying rapt attention, you’d already realize that injection molding can design thin-walled, complex shapes and intricate geometries and dimensions. The precision and tight tolerant capability of the injection molding process allow it to explore diverse designs. Meanwhile, the blow molding method is limited in design complexities but can still handle some complex designs

A manufacturer can decipher what method accommodates its design flexibilities based on the project requirements. The blow molding technique is able to design certain shapes and sizes but not all, at least not up to what the injection molding technique can handle.

3.4 Production Efficiency and Cycle Time

Taking into account the production efficiency and cycle time of blow molding and injection molding, a method that has the fastest completion rate and the lowest turnaround time is preferable. And this is the injection molding method. The injection molding process has shorter steps and faster cooling compared to other molding techniques and innovative approaches like 3D printing technology

Blow molding has a few more steps in the production cycle. For stages such as the air pressure stage, where a possible leak in the product is checked, removing excess material in the head and tail sections is often necessary. The cooling process of both methods also varies, with injection molding taking the upper hand. 

3.5 Part Quality and Surface Finish

Part quality is as important as the other considerations that have been mentioned. This is where excellence in production technique is measured. The quality of the manufactured plastic part must be coherent with the surface finish. And the only technique that excels in flying colors in this regard is the injection molding technique. 

It exhibits accuracy in the part’s dimensions, tight tolerances for strength and durability, and proffers consistent geometries. On the other hand, the blow molding process is vulnerable to inconsistencies in its parison formations and air pressure inflation to allow it to take form. Nevertheless, with some post-molding fine-tuning, blow molding can be enhanced to manifest a smooth surface finish.

4. Industries and Applications

4.1 Industries Utilizing Blow Molding

Owing to the benefits blow molding offers, such as the ability to make hollow lightweight plastic components and its cost-effectiveness, quality, and long-lasting parts. 

It is typically sought after by industries like the automotive industry, which utilizes blow molding to make parts like fuel tanks, interior components, and air ducts. The consumer goods industry, where plastic household items like buckets are made, isn’t left out. 

In addition, sporting goods and children’s toys can adopt the blow molding method in manufacturing these items, relying on their pocket-friendliness and versatility. Moreso, the industry that benefits from blow molding the most has to be the packaging industry. 

The adoption of blow molding immensely supports the manufacturers of lightweight plastics such as bottles and containers. All the industries mentioned above have chosen the blow molding process as their preferred technique of plastic part production, and it is no surprise why. 

The automotive industry leverages its complex shape-making prowess, coupled with its strength-to-weight ability. Similarly, the packaging industry solely relies on the blow molding technique’s durability, delicate yet strong, and hollow part manufacturing capacity. 

4.2 Industries Preferring Injection Molding

Some industries likewise trust the injection molding method to get the job done precisely and accurately, especially those big on detailing and speed. One such industry is the medical supplies industry. This industry counts on the efficiency of the injection molding process to manufacture some of its components. 

These components include medical implants, diagnostic equipment, and syringes. Manufacturing plastic products with tight tolerances and sterile and accurate parts is paramount in this industry, hence its trust in the process. Once again, the automotive and aerospace sectors depend on the accuracy of injection molding, comparable to computer-based manufacturing, like high-quality CNC machining

And not just that, precise dimensions and quality of product are highly recommended for plastic parts employed in these industries. Bumpers, dashboards, and other exterior features for the automobile industry apply injection molding and exterior and interior components for aerospace. Some aspects of mobile phones and computers are also majorly fabricated with the injection method. 

That represents the application of the injection molding method in the electrical industry. Consequently, some consumer goods items are manufactured by injection molding. 

Industry standards and regulations can also determine what technique to deploy to meet standards and quality certification.


After all the blow molding vs. injection molding information highlighted in the guide, you should understand now that blow molding is typically done by extrusion. In contrast, injection molding is directly injected into the molds designed for specific plastic production. 

Injection molding and blow molding, though different, are similar as well. They both accommodate thermoplastics in their respective manufacturing ideas. This is why a manufacturer should carefully understand the task at hand before selecting a process to employ. 

However, they can manufacture complex designs, even if one method is more suited. In addition, they are crucial to part production in numerous industries. Some include automotive, aerospace, consumer goods, packaging, electrical and medical industries, hence, their indispensability. And some industries prefer one method to the other, depending on the plastic production to be carried out. 

We hope this post helps you make an informed decision when deciding on what method to deploy in your next project. We will gladly help you further should you need our expert opinion or service. Or do you? 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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