Plastic Molding Method: Blow Molding

Material that most used for blow molding including PVC, PC, PP, and PS.

Blow molding is a molding method which mainly applied for manufacturing hollow, bottle-shaped or immense, large-size product.

E.g. Packaging of seasoning, shampoo, detergent, or water bottle, some example of product with large size including trash can, barrel of gasoline, or even Intermediate Bulk Container (IBC Container) which can contain 1 ton of chemical material.



1. The wall thickness of finish product is thin, it aids in the thrift of the material and conduce to the decrease of the cost.

2. Various kinds of material can be used on developing the mold, the cost is affordable as well.

3. Capable to make large hollow products, or those which have complex shape.




1. Size is lack of precision.

2. The wall thickness of the finish product is hard to control and sometimes molded uneven.

3. Flow line occurs easily, the surface is normally rough.



1. Not suitable to be used to make product with small size or fine structure.

2. Not suitable to be used to manufacture bottle-shaped product which has handle.


Blow molding can be divided into two categories:

A. Extrusion Blow Molding

Be seem as the oldest blow molding method, the capacity of the final product is range from 1 ml to 3 kl, the shape of the hollow product can be multilayer, thin wall thickness, or in complex shape, but the parting line and flash is occurred easily, the size rim and screw thread is not precised.

However, because of the new technique including thickness controller and design of coreless, such problems have been solved gradually these decades.


Molt the plastic material previously, then form cylindrical parison by the material, when the length meets the requirement, cut a section of the parison out, and ensure both ends has been pinched at the fixed position in the blowing mold. Next, close the mold and keep blowing the air into the cavity until the shape and size become same as the mold cavity, maintain the pressure and decrease the temperature, after cooling down, open the mold and demold the plastic article.


B. Injection Blow Molding

Typically applies to mass production of small-sized container or single served wide mouth bottle, yet the shape must not be too complicated, and the capacity must be between 5 ml and 500 ml.


Injection blow molding is a combination molding process, at first, the prototype of plastic article is made by injection molding, and then the prototype is transferred into blow molding part and continues the production with above mentioned extrusion blow molding process. 


Comparison of the two methods:

Injection blow molding is similar to extrusion blow molding, both ways are used to make hollow plastic articles.

However, injection blow molding is considered as a better way since it can effectively solve the problem of parting line and molding uneven, with injection blow molding, flash can be rarely found, material is less wasted, size is more precised as well, furthermore, the production is automatic easily.

**The information is for references only, blow molding is not available in Ji-Horng Plastic Co., Ltd., if you are interested in injection molding service, please feel free to contact us, thank you!**