Single-stage vs Two-stage blow molding

Single-stage vs Two-stage blow molding

The FMCG market is constantly changing, so businesses must also flexibly adapt to the increasingly shortened product life cycle. Production costs are increasing, so one of the solutions is to cut packaging costs to maximize profits.

By understanding that, packaging manufacturers are constantly improving technology to reduce the number and cost of mold production. Therefore, today’s PET bottle production includes two main methods (single-stage blow molding and two-stage blow molding). Enterprises need to choose a suitable one for the product’s productivity, shape, size, quality, and quantity. In the following article, DuyTanMold will analyze the differences between these two forms.


A single-stage process allows manufacturers to create preforms and blow them on the same machine.

The transformation of the raw materials into a bottle using the single-stage follows the procedures outlined below:

  • Dehumidifying and drying of PET materials.
  • Melting and injecting of the raw materials into the preform mold through the injection nozzle.
  • Cooling of the molten material in the preform mold to 120 ° Celsius
  • Transfering the hot preform mold to a bottle mold to begin the stretch molding.

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Advantages of single-stage blow molding

Since preform molding and bottle blowing are in the same machine, the heating and heat-insulating processes are performed in a closed system without exposure or collision with other objects. As a result, the bottle can maintain a clean, glossy, and intact surface. It is suitable for manufacturing products with high aesthetic requirements. Most used in the beauty industry, such as cosmetic containers, essential oils, body lotions, etc. Bottles can be produced with different materials such as PET, PP, HDPE, and PC.

  • The system is compact and flexible.
  • The blown bottle product is qualified, aesthetic, and less prone to stains and scratches.
  • Suitable for projects with low or medium output.
  • Control the output and production process of preform because there is no need to store semi-finished products.
  • Less expensive in comparison to two-stage machines.
  • Easier to blow complex shapes than 2-stage blow molding.

Disadvantages of single-stage blow molding

It is hard to conduct quality checks on the preform before blowing. Therefore, the operator needs to be knowledgeable about pressing and blowing to control defects caused during pressing or blowing. This method requires more peripheral equipment for both pressing and blowing, is more susceptible to climate influences, and requires more space to hold bottles.

  • Long cycle time.
  • Restriction in the bottle design
  • Suitable for small-sized products.
  • The machine operator should have technical expertise in both pressing and blowing.
  • Inefficient blow station due to injection station having more precedent over cycle time.


In this method, the plastic is molded into a fully-cooled preform in the first machine. The preform is cooled and stored as a semi-finished product. When there is a need for bottle production, the preform is reheated to the bottle-blowing temperature and transferred to the bottle-blowing process.

This process follows the procedures outlined below:

  • Drying PET materials.
  • Injecting molten raw materials into the preform mold by the injection machine.
  • Cooling of molten PET to room temperature.
  • Processing of preform by a finishing machine.
  • Transferring of the preform to reheating stretch blow molding machines.
  • Blowing high-pressure air into bottles with the use of metal blow molds.
  • Conducting bottle blowing process.
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Advantages of two-stage blow molding

During the reheating process, engineering can adjust the heating position, heating range, and heating power to suit different PET bottles and preforms. This allows the preform to be stretched evenly to produce bottles of uniform thickness. Therefore, it is suitable for manufacturing high-yield, lightweight, and cost-effective bottles such as beverage bottles, etc. Bottle manufacturers do not need to invest in preform molding. They can buy available preforms in the market to save costs when machining output is low. Blowers can also be integrated into plant filling lines. In addition, the separation helps the manufacturer optimize the seasonal characteristics, produce embryos first, and store or trade embryos separately while waiting for the next business season.

  • Flexibility in the production process.
  • Short cycle time.
  • We can stop at any time in the process.
  • The wall thickness is better for round bottles.
  • The billet and bottle can be sold separately.
  • Suitable for producing in large volumes.

Disadvantages of two-stage blow molding

Since the pressing and blowing steps are separate, the preform will be stored, transported, and aligned before blowing. The surface of the preform may be scratched by impact and still be visible after blowing. The difference between the inside and outside temperatures upon reheating makes it hard to manufacture flat bottles, square bottles, or bottles with handles.

  • High maintenance costs.
  • The floor space required is high.
  • Scratches may occur on the bottle.
  • Potential damage to the preform.


After analyzing the pros and cons of the two processes above, choosing the optimal one for an enterprise depends mainly on product quality and production output. Developing molds for products requires businesses to estimate output and calculate the appropriate number of molds.

At Duy Tan Precision Mold, we have more than 25 years of development with leading experts who are well trained by prestigious international organizations. We provide comprehensive advice and solutions to your mold problems.

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Duy Tan Precision Mold Co., Ltd

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