A successful blow molded product starts long before plastic enters the mold. The decisions made during the design stage can have a major impact on product performance, manufacturing efficiency, material use, tooling requirements, and overall production costs.
That is why blow molding design should focus on more than just creating the right shape. A well-designed part must also be practical to manufacture consistently and efficiently.
Whether you are developing a new plastic component or improving an existing product, understanding the fundamentals of design for blow molding can help prevent costly changes later in the production process.
In this blow molding design guide, we will explore several important factors that can help improve part quality while keeping manufacturing costs under control.
Why Blow Molding Design Matters
Blow molding is widely used to manufacture hollow plastic products and components. The process allows manufacturers to create durable, lightweight parts in a wide variety of sizes and shapes.
However, a design that looks great on a computer screen is not automatically optimized for manufacturing.
Small design decisions can affect:
- Wall thickness
- Material distribution
- Part strength
- Cooling time
- Mold complexity
- Secondary machining
- Scrap rates
- Production cycle times
- Overall manufacturing costs
Addressing these factors during the design stage can make production smoother and help prevent unnecessary tooling changes or quality problems.
The earlier manufacturers and product designers collaborate, the easier it is to identify potential issues before moving into full-scale production.
1. Keep Wall Thickness in Mind
Wall thickness is one of the most important considerations in blow molded part design.
During the blow molding process, heated plastic is expanded against the walls of a mold. As the plastic stretches, certain areas of the product may naturally become thinner than others.
If the design includes extreme changes in geometry, sharp corners, deep sections, or areas that require excessive stretching, maintaining consistent wall thickness can become more difficult.
Uneven material distribution may lead to areas that are weaker than intended while adding unnecessary material elsewhere.
Designers should think carefully about where the part needs additional strength and how the geometry will affect plastic distribution during molding.
The goal is not necessarily to make every section exactly the same thickness. Instead, the goal is to create a design that uses material efficiently while still meeting the product’s structural and performance requirements.
Using only the material needed for the application can also help reduce blow molding costs, particularly across high-volume production runs.
2. Avoid Unnecessary Sharp Corners
Sharp corners may look simple in a CAD model, but they can create challenges during blow molding.
Rounded corners and gradual transitions generally allow material to distribute more evenly throughout a part. They can also reduce concentrated stress areas that could affect long-term product performance.
When possible, incorporating appropriate radii into the design can make the part easier to manufacture and improve structural consistency.
This does not mean that every blow molded product needs to be round. Complex shapes are possible. The important consideration is how the plastic will stretch and conform to the mold during production.
A small change to a corner, transition, or feature early in the design process may prevent a much more expensive tooling modification later.
3. Design for the Actual Application
One of the biggest mistakes in plastic part design is creating a component without fully considering how it will be used.
Before finalizing a blow molded part, designers should consider the conditions the product will experience throughout its service life.
For example:
- Will the part be used indoors or outdoors?
- Will it experience temperature changes?
- Does it need impact resistance?
- Will it carry weight?
- Will it be exposed to chemicals or moisture?
- Does it need to connect with other components?
- Will people regularly handle or move it?
- Are appearance and surface finish important?
A component used in outdoor equipment may require different design and material considerations than one used in seating, construction equipment, agriculture, automotive applications, or consumer products.
Starting with the real-world performance requirements helps engineers avoid both under-designing and over-designing a product.
Over-design can be expensive. Adding more plastic, complex features, or unnecessary secondary operations may increase manufacturing costs without providing meaningful benefits.
The most effective blow molding design balances performance, durability, manufacturability, and cost.
4. Choose the Right Plastic Material
Material selection can affect nearly every aspect of a blow molded product.
Different plastic resins offer different levels of stiffness, impact resistance, chemical resistance, flexibility, temperature performance, appearance, and cost.
Common materials used for blow molded products can include polyethylene and polypropylene, among others. The best material depends on the specific requirements of the application.
Choosing a material simply because it worked for another product may not always be the best strategy.
Instead, consider questions such as:
- What type of load will the part experience?
- How rigid does the product need to be?
- Will it be exposed to sunlight or weather?
- Does the application require chemical resistance?
- Are there specific weight requirements?
- What surface appearance is required?
- What is the expected product lifespan?
Material selection should ideally happen alongside the design process rather than after the design is already complete.
Selecting an appropriate material can improve product performance while helping avoid unnecessary resin costs.
5. Simplify the Design Where Possible
Complexity usually comes with a price.
Additional features may require more complicated tooling, longer production cycles, additional trimming, machining, assembly, or specialized handling.
That does not mean complex blow molded products should be avoided. Modern custom blow molding can accommodate a wide range of shapes and requirements.
However, every design feature should serve a purpose.
During the design review process, ask whether certain elements can be simplified without affecting the function of the product.
Simplifying a design may result in:
- Easier manufacturing
- Less material usage
- Reduced tooling complexity
- Faster cycle times
- Fewer secondary operations
- More consistent parts
- Lower production costs
Sometimes a seemingly small design change can produce meaningful savings when multiplied across thousands of parts.
6. Consider Parting Lines Early
The parting line is the location where the two halves of the blow mold come together.
Its position can influence both the appearance and manufacturability of the finished component.
Waiting until tooling development to consider the parting line can create unnecessary complications.
Instead, parting-line placement should be evaluated during the blow molded part design stage.
The location may affect trimming requirements, cosmetic surfaces, dimensional features, and how easily the finished product can be removed from the mold.
If certain surfaces need to remain visually clean or specific features require tight control, communicating those requirements early helps the manufacturer determine an appropriate tooling strategy.
7. Minimize Unnecessary Secondary Operations
Blow molding may only be one step in the manufacturing process.
Some parts require additional operations such as trimming, drilling, machining, assembly, finishing, or packaging before they are ready for use.
These secondary processes can add value when necessary, but they can also increase labor, equipment requirements, handling, and production time.
A strong design for blow molding approach considers secondary operations from the beginning.
For example, designers may be able to modify certain features to reduce the amount of machining required after molding.
The goal is not always to eliminate secondary operations completely. Instead, manufacturers should determine which processes are necessary and where the design itself can make production more efficient.
Reducing unnecessary processing steps is one practical way to control the total cost of a custom blow molded product.
8. Use Prototypes and Design Reviews Before Full Production
One of the most expensive times to discover a design issue is after production tooling has already been completed.
Design reviews and prototypes provide an opportunity to evaluate a product before committing to full-scale manufacturing.
They can help identify potential concerns involving:
- Fit
- Function
- Geometry
- Material selection
- Wall thickness
- Assembly
- Manufacturing feasibility
- Secondary operations
A prototype does more than demonstrate what a product will look like. It can provide useful information about how the design may perform in the real world.
Changes made during development are typically easier to manage than changes required after a project reaches production.
Working with an experienced blow molding manufacturer during this stage can also help designers identify opportunities they may not see from the CAD model alone.
9. Design With Production Volume in Mind
Production volume is another important factor in blow molding design.
A product expected to run in high volumes may justify design or tooling decisions that improve cycle time by even a small amount. Over a large number of production cycles, small efficiency improvements can add up.
For lower-volume projects, manufacturers may prioritize different cost considerations.
Knowing the expected annual volume allows the design and manufacturing teams to make more informed decisions about tooling, automation, materials, finishing, and assembly.
It is also helpful to think beyond the first production order.
If demand increases, will the design be able to scale efficiently?
Planning for future production requirements can prevent expensive redesigns as the product grows.
10. Involve Your Blow Molding Partner Early
Perhaps the most important recommendation in this blow molding design guide is simple: involve your manufacturing partner early.
Product designers understandably focus on function, appearance, and customer requirements. Blow molding specialists bring another perspective—the realities of manufacturing the product repeatedly, efficiently, and consistently.
Early collaboration can help identify ways to improve:
- Manufacturability
- Material distribution
- Mold design
- Part strength
- Production efficiency
- Tooling requirements
- Secondary operations
- Overall cost
This type of collaboration can be especially valuable when developing a new product or converting a component from another manufacturing process.
Instead of waiting until the design is considered finished, bringing manufacturing expertise into the development process can reduce revisions and create a clearer path from concept to production.
How Better Blow Molding Design Can Reduce Costs
Reducing manufacturing costs does not necessarily mean choosing the cheapest material or removing important product features.
The best cost reductions often come from improving efficiency.
For example, an optimized design may use less resin while maintaining strength. Another design change could reduce machining requirements. A more manufacturable shape may improve consistency and decrease scrap.
Potential cost-saving opportunities include:
- Optimizing material usage
- Simplifying tooling
- Improving production cycle times
- Reducing scrap and rejected parts
- Limiting unnecessary machining
- Simplifying assembly
- Improving packaging efficiency
- Preventing late-stage tooling modifications
Looking at the entire manufacturing process provides a more accurate picture of cost than focusing only on the price of the molded part.
Frequently Asked Questions About Blow Molding Design
What makes a good blow molded part design?
A good blow molded part design balances function, durability, material usage, manufacturability, and cost. Appropriate geometry, wall thickness, corner radii, material selection, and secondary operations should all be considered before production begins.
How can I reduce the cost of a blow molded product?
Cost reductions can come from simplifying the design, optimizing material usage, minimizing unnecessary secondary operations, improving manufacturability, and identifying potential issues before tooling and full production.
Why is wall thickness important in blow molding?
Plastic stretches as it is formed inside the mold, which can create variations in wall thickness. Designing with material distribution in mind helps ensure that critical areas have the strength needed for the intended application.
When should a blow molding manufacturer become involved in product design?
Ideally, a blow molding manufacturer should be involved as early as possible. Early design assistance can help identify manufacturability concerns and potential cost-saving opportunities before expensive tooling decisions have been made.
Improve Your Next Blow Molded Product With the Right Design Support
Good blow molding design is about finding the right balance between performance and manufacturability.
Considering wall thickness, material selection, geometry, tooling, secondary operations, prototypes, and production volume early in the process can help produce stronger, more consistent parts while controlling costs.
Most importantly, manufacturers should not treat product design and production as completely separate stages.
Collaboration between product designers, engineers, and an experienced custom blow molding partner can uncover opportunities to improve a design before they become expensive problems.
At Blow Molded Solutions, our team works with customers to support custom blow molding projects from design and prototype review through production and secondary operations. Whether you are developing a new product or looking for ways to improve an existing blow molded component, involving an experienced manufacturing team early can help create a smoother path to production.
Ready to discuss your next custom blow molding project? Contact Blow Molded Solutions to learn how our team can help bring your design from concept to production.