Material selection is one of the most important—and most overlooked—decisions in injection molding.
The plastic you choose doesn’t just determine how your part performs. It directly impacts:
- Cost
- Manufacturability
- Lead time
- Tool making strategy
- Long-term reliability
For engineers and procurement teams alike, choosing the right material is a balancing act between performance requirements and total cost of plastics manufacturing.
At Montrose Molders Corp, we work with OEMs every day to evaluate material options and identify opportunities to improve both performance and cost.
This guide walks through how to make the right decision.
Why Material Selection Matters in Injection Molding
In injection molding, material selection influences nearly every aspect of production:
- Part performance (strength, flexibility, durability)
- Injection mold design (shrinkage, cooling, wear)
- Cycle time and cost
- Tool life and maintenance
Choosing the wrong material can lead to:
- Higher costs
- Quality issues
- Production delays
Choosing the right material creates a foundation for efficient, scalable plastics manufacturing.
Common Plastics Used in Injection Molding
Understanding the most widely used materials is the first step.
ABS (Acrylonitrile Butadiene Styrene)
- Strong and impact-resistant
- Good surface finish
- Common in consumer and industrial applications
Polypropylene (PP)
- Lightweight and cost-effective
- Excellent chemical resistance
- Ideal for high-volume applications
Polyethylene (PE)
- Flexible and durable
- Good for containers and tubing
- Lower strength than engineering resins
Nylon (PA)
- High strength and wear resistance
- Good for mechanical components
- Absorbs moisture, which can affect performance
Polycarbonate (PC)
- High impact strength
- Transparent options available
- Higher cost but excellent durability
Each material offers different advantages, and the right choice depends on your application.
Key Factors in Material Selection
1. Mechanical Requirements
Start with how the part needs to perform:
- Does it need to withstand impact?
- Does it require flexibility or rigidity?
- Will it experience load or stress?
Choosing a material that meets—but does not exceed—these requirements is critical for cost control.
2. Environmental Conditions
Consider where and how the part will be used:
- Exposure to heat
- UV light
- Chemicals
- Moisture
Some materials perform well in controlled environments but degrade quickly in harsh conditions.
3. Cost Considerations
Material cost is often evaluated per pound—but that’s only part of the picture.
You should also consider:
- Cycle time (some materials process faster)
- Scrap rates
- Tool wear
- Long-term reliability
A slightly more expensive material may reduce total cost through better process efficiency.
4. Processing Behavior
Different materials behave differently during injection molding:
- Flow characteristics
- Shrinkage rates
- Cooling requirements
These factors influence:
- Injection mold design
- Tool making complexity
- Production efficiency
How Material Selection Impacts Tool Making and Injection Mold Design
Material selection plays a direct role in tool making and mold performance.
Shrinkage
Each material shrinks differently as it cools, which affects:
- Mold dimensions
- Part accuracy
Tool Wear
Some materials—especially filled resins (glass-filled, mineral-filled)—are abrasive and can:
- Increase wear on the injection mold
- Require hardened steel tooling
Cooling and Cycle Time
Materials with higher heat resistance often:
- Require longer cooling times
- Increase cycle time
This directly impacts cost per part.
Common Material Selection Mistakes
Many programs run into issues due to avoidable material decisions.
Over-Specifying Materials
Using an expensive engineering resin when a commodity material would suffice can significantly increase cost.
Ignoring Manufacturability
Some materials are difficult to process, leading to:
- Higher scrap rates
- Longer cycle times
- Increased variability
Not Considering Tooling Impact
Material choices that increase tool wear or complexity can raise both tool making costs and long-term maintenance expenses.
Where Cost Savings Are Often Found
Material optimization is one of the most effective ways to reduce injection molding costs.
Opportunities Include:
- Switching from engineered resins to commodity materials where possible
- Using filled vs unfilled materials strategically
- Reducing part weight through design changes
- Incorporating recycled or regrind material where appropriate
These changes can deliver meaningful savings without sacrificing performance.
How to Get Material Selection Right
The most successful programs approach material selection as a collaborative process.
Best Practices:
- Engage your injection molding partner early
- Balance performance requirements with cost targets
- Validate materials through testing and prototyping
- Consider both short-term and long-term production needs
At Montrose Molders Corp, we work closely with customers to evaluate tradeoffs and identify the most efficient path forward.
Why Material Selection Is a Strategic Decision
Material selection is not just an engineering decision—it’s a business decision.
The right material can:
- Reduce cost
- Improve product performance
- Accelerate production
- Extend tool life
The wrong material can create ongoing challenges that impact your entire supply chain.
Final Thoughts
In injection molding, material selection sits at the intersection of:
- Engineering
- Tool making
- Plastics manufacturing
- Cost optimization
Making the right choice requires understanding how all of these elements interact.