Blow Molding or Injection Molding: Which Method Is Best?

choosing injection molding or blow molding for custom plastics

Manufacturing plastics can be done in a variety of ways, but choosing the right method can be difficult. While you want to have a product made quickly and affordably, you don't want to compromise quality and choosing the wrong manufacturing method to create a product can lead to serious problems. When it comes to molding and shaping plastic into complicated designs, injection molding and extrusion blow molding are two popular methods, but does one produce a better result than the other? Our injection molding company is looking at how each process works, the benefits and challenges each one presents and which products are more likely to be made through blow molding and which are more likely to be a product of injection molding.

Understanding the Injection Molding Process

Once a prototype is approved, a double-sided mold made from steel, aluminum, or a beryllium-copper alloy is fabricated. Thermoplastic pellets are melted to a liquid, and poured into high-powered injectors that force the plastic into the mold with high pressure and power to ensure every detail in the mold is captured in the final result. Once the mold is cool and the plastic has hardened, the completed plastic component is ejected and finished.

Benefits and Challenges of Injection Molding

Injection molding offers a variety of benefits but there are also some challenges and drawbacks that mean it may not be ideal for every product.


  • Cost: While the tooling is expensive, the per-unit cost ends up being quite low.
  • Detail: The tooling can be fabricated with incredible detail, so if a complex or advanced design is needed, it's easier to achieve with this method.
  • Efficiency: Multi-cavity molds can be created to quickly produce thousands of identical parts or components.
  • Small components: While thermoforming and other methods are ideal for large pieces of plastic, injection molding is idea for small pieces.
  • Minimal waste: Any unused plastic can be easily recycled, and because the programming is so precise, there's little left over to be trimmed and thrown away.


  • Upfront cost: Injection molding requires heavy-duty tooling that can have a longer up-front lead time to produce and be more expensive to design and fabricate;
  • Size: While small to medium items can be produced rapidly, large pieces can be challenging and may require multiple injectors to fill one mold.
  • Hollow plastics: While hollow plastics can be created through injection molding, the outer walls may be slightly thick.

Understanding the Extrusion Blow Molding Method

Extrusion blow molding is a process that begins by melting down a thermoplastic and shaping it into a hollow tube, called a parison. The parison is clamped into a mold and pressurized air is blown into the opening at the top of the tube. The air pushes the plastic outward (similar to blowing up a balloon) and it forms around the walls of the mold. Its very similar to glass blowing.

In addition to extrusion blow molding, injection blow molding and injection and injection stretch blow molding are similar methods though aren't used as often.

Benefits and Challenges of Blow Molding

Like injection molding, blow molding has some excellent qualities and some that make it challenging and not ideal for every project.


  • Cost: Unlike injection molding, the tool and die can be made of inexpensive materials so the cost is less;
  • Quick: Thin, hollow plastic pieces can be created and produced fairly quickly.
  • Detailing: The mold can be designed with heavy detailing and can be used for complex parts;


  • Limited use: Extrusion blow molding is only used for hollow parts;
  • Strength: The corners and areas where the walls are thin have close tolerance and can be weakened;

Choosing the Method of Production That's Right for Your Company

Both processes have benefits and challenges, but the two aren't interchangeable. Blow molding is only used for hollow items like plastic bottles, jugs, and beakers, whereas injection molding is primarily used to manufacture solid pieces or even hollow pieces with thicker walls. Consider the product or component you need and you'll have your answer as to which one you should choose.

Contact Us for High Quality Injection Molding

If you need accurate, high-quality custom plastics created through injection molding or thermoforming, we can help. We work with all types of industries in the Southeast and Mid-Atlantic, including North CarolinaPennsylvaniaMarylandTennesseeGeorgia, and Virginia. To learn more, reach out to our team today.

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