Plastics For Blow Molding Sourcing Guide

Types of products made with blow molded plastics

As you saw in the introduction to this guide, plastics for blow molding are incredibly commonplace. Other common products you will have encountered that have been produced by blow molding include:

• Construction barrels
• Road safety barriers
• Stadium seating
• Water coolers and bottles
• Garden water butts and buckets
• Car dashboards
• Car washer fluid container
• Car trims and seating
• Car cooling system and washer reservoirs
• Children’s toys, such as blocks, bats, etc
• Washing machine and dishwasher reservoirs
• Medical instruments, containers, and components
• Tubing and seals
• Marine buoys
• Industrial containers for bulk goods
• Packaging
• …and many more

It’s likely that blow molded plastics are used somehow in your industry, so let’s explore the common blow mold material types on offer.

The 3 blow molding processes

Blow molding is a fully automated process which is capable of producing hollow and very large items, such as the bottles below. Injection molding is similar, but the products and parts made are generally solid instead of hollow:

There are basically three types of blow molding processes:

• Extrusion blow molding (EBM)
• Injection blow molding (IBM)
• Injection stretch blow molding (ISBM)

Here are some summaries of these three processes to allow you to get a better understanding of how they differ.

Extrusion Blow Molding

Extrusion Blow Molding (EBM) is a manufacturing process used to create hollow plastic components, such as bottles and containers. The procedure begins by heating plastic material, often a thermoplastic polymer, and pressing it through a die to form a parison or tube-like structure. This mixture is then transported to a mold, where it is shaped using air pressure. The purpose of the mold is to form the plastic around the interior chambers, so producing the desired hollow product. 

EBM is utilized to manufacture a variety of components, including huge containers, industrial containers, and small, complex components. The method is renowned for its adaptability, allowing producers to create components with varying shapes, sizes, and wall thicknesses. The utilization of a single machine and tooling configuration makes EBM a cost-effective and efficient choice for large manufacturing.

In addition, EBM may be accomplished using a number of materials, such as high-density polyethylene (HDPE), polypropylene (PP), and polyvinyl chloride (PVC), making it a flexible option for various sectors.

Here’s an image showing the extrusion blow molding process (image source):

Injection Blow Molding

Injection Blow Molding (IBM) is a technique used to manufacture hollow plastic items such as bottles, jars, and other containers. Injecting molten plastic into a mold to create a preform begins the process. This preform is then moved to a second mold, where it is heated and blown under air pressure into its final shape. 

The procedure is capable of generating components with precise details, close tolerances, and thin walls. IBM is frequently used to manufacture small to medium-sized containers, particularly those manufactured from high-density polyethylene (HDPE) and polypropylene (PP). 

The IBM method is renowned for its great efficiency and low waste, making it a cost-effective solution for the mass manufacture of plastic containers. In addition, IBM permits simple color and design modifications, making it a versatile solution for producers who wish to offer a wide range of products.

Here’s an image showing the injection blow molding process (image source):

Injection Stretch Blow Molding

Injection Stretch Blow Molding (ISBM) is a manufacturing process used to create high-quality, hollow plastic components, such as bottles and containers. The procedure begins with the injection of molten plastic into a mold to create a preform. This preform is then moved to a second mold, where it is heated and stretched using air pressure to achieve its final shape. 

Stretching plastic increases its molecular orientation, making the end product stronger and more transparent. ISBM is a two-step technique that combines the advantages of injection molding and stretch blow molding. The final product has a uniform wall thickness, great impact resistance, and outstanding transparency. 

ISBM is typically employed in the production of small to medium-sized containers, particularly those produced from polyethylene terephthalate (PET) and other thermoplastic polymers. The process is also renowned for its high productivity and low waste, making it a cost-effective method for producing plastic containers in large quantities. 

ISBM is frequently employed for packaging applications in industries like food and beverage, medicines, and consumer goods.

Here’s an image showing the injection stretch blow molding process (image source):

Is there a manufacturing and process cost difference between the different blow molding techniques?

Yes, there is a difference in manufacturing and process costs between the different blow molding techniques.

Due to fewer equipment and tooling needs, extrusion blow molding tends to have cheaper startup costs, but higher production costs for larger and more complex items.

For the mass manufacture of small to medium-sized containers, injection blow molding’s low waste and high productivity makes it a cost-effective method.

Injection stretch blow molding has greater startup costs due to the need for more complex equipment and tools but reduced production costs because of its high productivity and consistent product quality.

Ultimately, the cost difference will depend on the specific requirements of each project and the chosen blow molding technique.

Blow mold material typically used in blow molding

There are a lot of suitable blow molding plastics which is great for diversity when it comes to product application and material selection for importers. You are not too restricted in terms of environmental limitations, impact resistance, weight constraints, or cost due to the wide range of polymer options.

Let’s have a look at 8 of the most widely used plastics for blow molding:

1. Acrylonitrile Butadiene Styrene (ABS)
2. High-Density Polyethylene (HDPE)
3. Low-Density Polyethylene (LDPE)
4. Polypropylene (PP) 
5. Polyamides (PA) also known as Nylon
6. Polyethylene Terephthalate (PET)
7. Polyvinyl Chloride (PVC)
8. Thermoplastic Elastomers (TPE)

1. Acrylonitrile Butadiene Styrene (ABS)

ABS is a popular engineering polymer that is opaque when used as blow mold material, although it can be easily colored. It is one of if not the most popular engineering plastics as it has numerous beneficial properties and is affordable.

Blow molded plastics made from ABS are often used for consumer electronic enclosures, sports helmets, sanitation pipes, automotive enclosures and components, and many more.

ABS is less chemically-resistant than some other polymers, so bear in mind your product’s application if it will involve a lot of chemical contact. It is very tough, though, so durable products could benefit from using it. Finally, ABS is recycling code 7 and it is quite difficult to recycle as well, though, so manufacturers who are taking very strict control over their product’s environmental impact may choose to select a more easily recyclable polymer.

ABS Benefits

• High impact resistance which makes it suitable for applications where knocks and bangs can be expected. Also a good insulator from heat and electricity.
• Excellent surface finish and high gloss can be achieved, so it is a good polymer for higher-value products with plastic enclosures.
• Great material for injection molded parts, as it is easy to injection mold and a high level of detail can be achieved.
• Good level of accuracy and dimensional stability as long as it is kept within the working temperature range.
• Can be used in 3D-printing.
• Can be recycled and reused in molding.
• One of the more cost-effective polymers at just $1.55/lb.

ABS Drawbacks

• Not appropriate for high-temperature environments or working conditions.
• Poor resistance to solvents and other chemicals.
• Will produce toxic fumes when burnt (although some grades are quite flame resistant).
• Does not perform well under repeated stress and strain – will fracture over time.
• Limited use for outdoor products as it is affected by UV light.

2. High-Density Polyethylene (HDPE)

HDPE is at the top of the list when it comes to the most commonly used plastic in the world and, unsurprisingly, it is also top out of the blow molding plastics used by manufacturers, too. It’s also commonly recycled (it’s recycling code 2), so is, arguably, a somewhat ‘greener’ option.

Products made from HDPE include bottles for consumer liquids such as shampoos and motor oils, as well as coolers, fuel tanks, carrying cases, and a plethora of other products. With exceptionally good blow molding properties, HDPE is very easy to process and is very cost-efficient as well as readily taking on most colors. It is also FDA-approved and some say it is the safest plastic available for use in things like food packaging and containers.

HDPE Benefits

• HDPE is very easy to work with and fabricate.
• Can take on most colors and a large range of textures.
• FDA-approved for use in food applications.
• It is plastic recycling code 2 and is recycled at the kerbside in many countries.
• Good chemical and weather (with the exception of UV) resistance.
• Only melts at very high temperatures.
• A reasonably stiff plastic (which could also be negative in some cases).
• Cost-effective at approx. $0.70/lb.
• Impact resistant and strong.

HDPE Drawbacks

• Will burn at the right temperature.
• Easily degraded by UV exposure.
• Does not bond together as easily as some polymers.
• Not biodegradable (typical of oil-based polymers).
• Can crack when put under stress.

3. LDPE

LDPE, the lower-density and thinner cousin of HDPE, is commonly used for squeeze bottles, flexible lids, tubing, traffic guides, component bags, cables, and packaging films. It is most commonly used to produce plastic bags making LDPE a very high-content user of blow molding plastics. It is also molder-friendly, translucent and easily colored, and chemically inert which makes this plastic a very popular choice. Like HDPE, it is also low cost, another reason for its popularity.

LDPE Benefits

• Transparent or can be colored easily.
• Very flexible, yet also tough.
• Impact resistant.
• Resists chemicals well.
• Can be recycled (even films at many supermarkets) and is recycling code 4.
• It’s a cost-effective polymer at $0.85/lb.

LDPE Drawbacks

• Less stiff and strong than HDPE, therefore even more prone to cracking under stress.
• Does not tolerate extremely high or low temperatures.
• Very little UV resistance.
• Gas permeable.

4. Polypropylene (PP)

Polypropylene is the world’s second most used plastic, particularly when it comes to injection molded products, and its popularity stems from its incredible versatility. PP is a very similar plastic to HDPE but has higher stiffness properties, it is less dense and can withstand higher temperatures. Typical blow molded plastic products produced from PP are squeeze bottles and containers.

PP Benefits

• Very flexible, often used for living hinges.
• Light and low-density.
• Highly waterproof.
• Can be used in 3D-printing.
• Acid resistant and good for storing acidic chemicals and liquids.
• Easy to mold and can be reused and re-molded readily.
• Low-temperature resistant.
• Corrosion resistant, so popular for use in piping.
• Low cost at $0.75/lb.

PP Drawbacks

• Not easy to bond, so must usually be treated before painting.
• Poor UV resistance.
• Very flammable and will catch fire at the relatively low temperature of 260 C.
• Will crack in hot environments.

5. Nylon / Polyamide (PA)

Nylon has great toughness, chemical, and heat resistance properties making this one of the favored plastics for blow molding of the automotive industry; and, it’s affordable, too.

Examples of such products would be under-the-hood components, dashboards, and electrical connectors. Nylon is also widely used in the medical industry and for computer parts, as well as for consumer electronics that need to be rugged such as DIY power tools.

Nylon Benefits

• Very tough and durable.
• Can withstand rain and splashes.
• Anti-static and so a good option for electronics.
• Able to withstand high temperatures of up to 300 Deg C.
• Easily modified in the raw state to improve its physical and operational properties.
• Good strength and hardness characteristics.
• Very good dampening properties, able to withstand shock loads and vibrations.
• Self-lubricating properties and a smooth surface finishes provide a low friction coefficient.
• It’s one of the more cost-effective polymers at $3/lb.

Nylon Drawbacks

• Will absorb moisture which degrades the nylon over time.
• Not biodegradable and its manufacturing process has a negative impact on the environment and may not be readily recycled.
• Poor resistance to acids and strong bases.
• Produces a toxic fume when burned with an open flame and it will melt and burn when subjected to, admittedly very high, temperatures.
• Not ideal for outdoor use as it is affected by UV light and water ingress.

6. Polyethylene Terephthalate (PET)

PET is one of the most handled blow molded plastics from a consumer point of view as this is what plastic bottles and food packaging for fruit, etc, as well as some textiles, are often made from due to it being a transparent, strong, and light polymer. If treated, it can even be used for food preparation and storage applications.

Like HDPE, PET is readily recycled and is recycling code 1.

PET Benefits

• Transparent like glass, but can be colored easily.
• Can be used for 3D-printing.
• Food-safe because it is non-reactive when in contact with foodstuffs.
• Waterproof.
• Odor and fume-free.
• Shatterproof.
• Very light.
• Melts instead of burning so can be recycled easily in this way (and is code 1).

PET Drawbacks

• Relatively poor tensile strength.
• Has a low heat resistance.
• A little more expensive compared with some other polymers here.
• Can crack if bent or exposed to very low temperatures.
• Has a low melting point which restricts its use in hot environments.

7. Polyvinyl Chloride (PVC)

PVC is commonly used in the production of shrink wrap for non-food product packaging, tubing, automotive seating and interior trims, window frames, and more, however, PVC is not as well suited to blow molding as some other plastics due to releasing hydrochloric (HCI) acid during processing and releasing residual vinyl chloride monomers after molding. This makes it a more difficult polymer to work with, although it has certain benefits depending on your application, especially if insulation is important for your product.

PVC Benefits

• Lightweight.
• Durable and long-lasting.
• Tough.
• Rigid.
• Very weather resistant.
• Great electrical insulator.
• Fire retardant.

PVC Drawbacks

• The chemicals in PVC can be harmful to human health.
• Not good for drinking water pipes.
• Poor UV resistance.
• Emits harmful hydrogen fumes when burnt.
• Not easily processed and recycled, and so not very green.

8. Thermoplastic Elastomers (TPE)

TPE is a thermoplastic ‘rubber’ and has numerous benefits over its natural cousin, not least the ability to blow mold various products from it due to how soft it is in comparison to most other polymers and the associated ease of fabrication (harder and tougher plastics are more difficult to work as they take more processing, whether that be heat or other things).  As a synthetic rubber, it has many applications such as automotive seals, bumpers, mats, and trims. Also removable cellphone covers, push-button and keyboard covers, seals, valves, tubing, suspension bushes, car shocks, footwear soles, and more.

Because it melts instead of burning it can be reused and recycled into new products which is better than some hard-to-recycle polymers.

TPE Benefits

• Non-toxic and doesn’t contain chemicals that are harmful to human health (can be food safe in some grades)
• Very soft.
• Very elastic and also tear-resistant.
• Good thermal properties and can withstand weather well.
• Takes on colors well when dyed.
• Good chemical resistance.
• Hardwearing.
• When ground down they can be used in 3D printing.
• Low energy to produce and can be reused fairly readily.

TPE Drawbacks

• Loses structural integrity by softening at high temperatures.
• Can deform when placed under continued stress or pressure.
• Loses its rubbery texture in extreme temperatures.
• Can be more expensive than some other polymers here.
• Needs to be dried before it can be processed.

Summary: Choosing plastics for blow molding

As blow molding is a very versatile process that can process a lot of different product types, you really need to understand your product and where it will be used, the environment it will be used in, and the geometry before settling on the blow mold material for your needs.

If the product can be processed by ‘blowing up a balloon,’ like a hollow bottle for example, then you should consider blow molding. If your product has complex shapes and features then you may want to consider injection molding instead.

As for the plastics for blow molding you can choose from, the list above is just a common selection, there are a lot more specialized plastics that can be selected, but as stated to start with, this is just an overview of some of the most common plastics used to start off your sourcing journey.

As ever, the team here at Sofeast are here to help you if you have any questions about blow molding, plastic selection for your products, or other production processes.

More plastics resources to explore

First, if you have any questions about plastic enclosures for electronics projects, please ask us any time.

You may also like these resources to help you source the right plastics for your needs:

• Guides and videos about thermoplastics
• How to Choose the Correct Outdoor Plastics for your next Product? (4 Guides)
• Sourcing Guides for Internal Use Plastic Mechanical Parts
• Plastic Enclosures for Electronics Projects (Plastics Sourcing Guide)
• The Plastic Injection Molding Process
• Guide To 3D Printing Rapid Prototyping
• 9 Types of Packaging (Benefits, Costs, Sustainability, and more) guide for Importers – including plastics!