What Is Hollow (Extrusion) Blow Molding?

Plastic hollow blow molding (Hollow Blow Molding) is a processing technology that uses compressed air to inflate molten plastic inside a mold, forming hollow products. It is one of the thermoplastic molding methods, widely applied in bottles, containers, pipe fittings, toys, fuel tanks, and more.

 

The term “extrusion blow molding” (sometimes simply called “blow molding”) is commonly used in the industry, and in most cases can be regarded as equivalent. In simple terms:

Blow molding = Air molding, though technically, blow molding encompasses a wider range of classifications and processes.

 

Core Process of Blow Molding

1. Plastic Melting

• Plastic pellets (such as PE, PP, PET) are heated until molten, preparing for molding.

 

2. Parison / Preform Production

Depending on the molding method:

• Extrusion Blow Molding (EBM): A hollow tube (parison) is directly extruded.
• Injection Blow Molding (IBM): A preform (bottle preform) is injection-molded first.
• Stretch Blow Molding (SBM): The preform is stretched axially before blowing, enhancing mechanical strength.
  
  

3. Parison Placement in Mold

• The parison or preform is placed into an open mold, which then clamps shut, preparing for blowing.

 

4. Inflation

• High-pressure air is injected, expanding the parison to fit tightly against the mold wall, forming a hollow structure.

 

5. Cooling & Demolding

• Once cooled and solidified, the mold opens and the finished hollow plastic product is removed

 

Common Blow Molding Types

1. Extrusion Blow Molding (EBM)

• Molten plastic is extruded into a tube and immediately blow molded.
• Applications: Detergent bottles, jerry cans, toys, canisters.

 

2. Injection Blow Molding (IBM)

• Preforms are first injection molded, then blow molded.
• Applications: Pharmaceutical bottles, small cosmetic bottles, precision bottles.

 

3. Stretch Blow Molding (SBM)

• Preforms are stretched axially and then blow molded, improving strength.
• Applications: PET bottles, water bottles, carbonated beverage bottles

 

4. Multi-Layer Co-Extrusion Blow Molding

• Multiple layers of materials are extruded simultaneously to enhance barrier properties or strength.
• Applications: Milk bottles, chemical packaging bottles, multi-layer oil bottles

 

Main Applications of Blow Molding

• Beverage bottles, PET water bottles
• Shampoo & detergent containers (HDPE)
• Oil jugs, pesticide bottles, lubricant bottles
• Automotive hollow parts (air ducts, fuel tanks)
• Plastic toys (hollow balls, figures)
• Industrial hollow drums, chemical barrels
• High-barrier food packaging containers (multi-layer co-extrusion)

 

Advantages of Blow Molding

• Ideal for hollow plastic structures
• Stable process with short cycle times
• Lower mold cost compared to other processes
• Compatible with a wide range of materials (PE, PP, PET, PVC, PC, etc.)
• Can integrate handles, threads, and multi-layer structures

 

Dih Hong Plastic，Professional Blow Molding Services

With years of experience in plastic hollow blow molding, Dih Hong Plastic excels in producing industrial containers, automotive parts, chemical containers, household packaging bottles, and functional multi-layer bottles.We provide:

• Customized mold design
• Small-batch sampling & mass production
• Technical consultation on multiple blow molding methods (extrusion / injection / stretch)
• OEM / ODM cooperation

 

Equipped with fully automated blow molding machines and strict process control, we are also experienced in multi-layer blow molding development and special-shape container design, meeting diverse application needs across food, chemicals, medical, automotive, and industrial packaging.