Blow Molding – Why, What and How

Blow molding is the process of melting plastic and extruding it into a hollow tube, called a parison, where high pressure air is blown to mold the plastic into a desired shape.

Class Plastics - Blow Molding

Blow molding is the process of melting plastic and extruding it into a hollow tube, called a parison, and  injecting high pressure air to form a container. It is the most common and widely used method in container manufacturing. And while there are many other methods available, blow molding is considered to be the most efficient and cost effective way to produce high volumes of packaging containers.

At Class Plastics, we believe that blow molding is an art as well as a science. As blow molding specialists, we offer a range of products that can be customised to address the most challenging problems and give our customers a competitive edge.

Why Blow Molding?

  • Less pressure equals less cost

Blow molding uses less pressure. Therefore, the machinery and molding costs are lower than other manufacturing process.

  • Higher production rate

Blow molding has a faster cycle than other manufacturing process. It is ideal for manufacturing large quantities. Traditionally, you can get one part done every one minute with blow molding, compared to one every 50 minutes using other methods.

  • Easily mold complex parts

Blow molding can easily mold complex parts, like handles and other asymmetrical shapes. You can easily customise your product because you have more design options.

Blow Molding vs Injection Molding

Unlike blow molding, injection molding involves melting plastic, and compressing it into a mold. When the plastic cools, it then takes the shape of mold.

Injection molding creates a solid path whereas blow molding creates an entry path that can be then filled with liquid. Blow molding produces hollow containers like bottles and milk jugs while injection molding produces solid plastic.

A bucket is made by injection molding because it does not have a small entry point whereas a milk container has to be blow molded to form its shape and create the small entry point for filling it with liquid.


As mentioned earlier, blow molding involves melting the HDPE resin and extruding it into a hollow tube, called a parison. The parison is then inserted into a mold, of a particular shape, to form the finished product. Ambient air is blown into the parison to inflate it and mold the plastic into the desired shape. Typically, this process takes around 30-90 second between parts.

The plastic is cooled with chilled water in the cavity through an aluminum tool. When it has cooled enough, the plastic is taken out of the mold.

As blow molding specialists, we can customise your product to have specific properties. Whether you just want to improve the look of your packaging or have a problem that you need to address, our custom molding guarantee, ensures you get the best product all the time.

For a quote or more information about our products, Contact Us today.

Posted in

Mario Nastri

Mario Nastri is currently a director/shareholder of Class Plastics Aust., Class Plastics QLD. & Class Packaging SA. In his past endeavors he has worked as a biochemist & physiologist at the University of Naples, Federico II 1993-1997, concentrating on aquaculture, marine pollution & during the winter months Cryogenics & IVF research & development, holding a Bachelor of Science majoring in Pharmacology & Biochemistry from Monash University. Mario also has a strong logistics background having managed a fleet of heavy vehicles which was part of a family owned business in the 1980’s & 90’s, transporting quarry stone, sand & asphalt for road surfacing. He has been with Class Plastics since 1999 & has extensive Blow molding knowledge which he has acquired over the past 20 years. He has extensive knowledge in managing a manufacturing business & overseeing a staff of 40 odd people across 4 states & 24 hour operations. He is committed to the continuous improvement of every department of the Class Plastics business, from improving manufacturing processes to creating energy via a 365Kw/1350 solar panel system installed 24 months ago.

Leave a Comment