How to Choose the Right Plastic for Your Injection Moulded Component
There are thousands of polymer grades available for injection moulding. In practice, most projects come down to a much shorter list. But getting material selection right matters more than most people expect, and the decision is better made during design than after tooling has started.
The material affects not just how the part performs in use, but how the tool needs to be designed, how the part shrinks, what tolerances are achievable, and what the component will cost over a production run. Here is a guide to the most common materials and how to think about the choice.
Why material selection should come before tooling
Different materials shrink at different rates as they cool in the tool. That shrinkage figure is one of the inputs used when designing the tool itself. If you change material after tooling has been cut, the dimensions of the tool may no longer produce parts that meet your tolerances.
Material choice also affects gate size, flow path design, wall thickness requirements, and cooling time. An experienced moulder will factor these in during the design stage, but only if material selection has been confirmed. The earlier in the process this is locked down, the better.
The most widely used materials and what they are suited for
ABS (Acrylonitrile Butadiene Styrene) is one of the most common engineering plastics. It is rigid, impact-resistant, and processes well, making it a reliable choice for housings, enclosures, and consumer product components. It accepts paint and surface finishes readily, and is widely available across a range of grades.
Polypropylene is valued for its combination of low weight, chemical resistance, and flexibility. It is used across a wide range of sectors and is one of the better materials for living hinges, where the material needs to flex repeatedly without fracturing. It is cost-effective at volume and is widely used in both FMCG packaging and industrial applications.
Polyethylene is known for its moisture resistance and softer feel compared to polypropylene. It comes in high-density and low-density forms, each with different characteristics. HDPE is stiffer and suited to structural applications, while LDPE is softer and more flexible, used where a degree of give is needed.
Nylon (Polyamide) is a strong, wear-resistant material used widely in engineering components. It performs well in applications involving friction, load-bearing, or repeated mechanical contact, such as gears, bushings, and clips. It is available in various grades including glass-filled variants where additional stiffness is required.
Polycarbonate offers high impact strength combined with optical clarity, making it the material of choice for lenses, light covers, and transparent guards. It is more expensive than commodity plastics and requires careful processing to avoid moisture-related defects, but for applications where transparency and toughness are both needed, it has few rivals.
Acetal (POM) is a precision engineering material with low friction, high dimensional stability, and good fatigue resistance. It is used in mechanical components where tight tolerances need to be maintained over time, including precision fasteners, pump components, and small moving parts. It is not suited to environments with strong acids or bases.
PEEK is a high-performance polymer for demanding applications. It retains its properties at elevated temperatures, resists a wide range of chemicals, and can be sterilised. It is used in aerospace, medical, and industrial applications where standard engineering plastics are insufficient, and it carries a cost premium to match.
Key questions to ask before choosing a material
What temperatures will the component experience in use? Some materials that perform well at room temperature soften or distort under heat. If the component sits near an engine, oven, or similar heat source, temperature resistance becomes a primary consideration.
What is the chemical environment? Fuels, oils, solvents, and cleaning agents all affect different plastics differently. A material that works well in one application may swell, crack, or degrade in another. Confirming chemical compatibility early avoids problems in the field.
What are the mechanical requirements? Stiffness, impact resistance, fatigue life, and whether the part needs to flex without breaking all point toward different material families. A component that needs to flex repeatedly has different requirements to one that needs to hold a fixed load.
Are there regulatory requirements? Food contact, medical device, and automotive applications all carry specific material requirements that go beyond performance properties. These need to be identified before material selection is finalised.
What is the expected production volume and price sensitivity? Higher-performance materials carry higher costs. For high-volume applications, even a small cost difference per kilogram adds up significantly across a production run.
Sector-specific considerations
In automotive applications, dimensional stability at temperature, resistance to fluids, and compliance with IATF standards all shape the material shortlist. The requirements are often more specific than in general manufacturing, and the consequences of failure in service are higher.
In industrial and engineering applications, wear resistance and load-bearing performance tend to be the primary considerations. Nylon, acetal, and glass-filled grades feature heavily in these applications.
In FMCG and packaging, cost, processability, and regulatory compliance drive most decisions. Cameron-Price has published a dedicated guide to FMCG materials for plastic injection moulding which covers polypropylene, polyethylene, and polystyrene in more detail for that specific sector.
Why material choice is a conversation, not a spec sheet
Material selection datasheets give you properties under controlled conditions. What they do not tell you is how that material will behave in your specific tool, with your specific wall sections, at your specific cycle time. That is where practical moulding experience matters.
A moulder who has worked across multiple sectors and materials can flag potential issues before they become production problems. They can suggest alternative grades, identify where a material switch might make the tool design simpler, or flag where the combination of geometry and material is likely to create challenges.
Cameron-Price offers a free initial consultation to help assess material requirements as part of the broader project scope. You can find out more through the design and development page or get in touch directly through the contact page to talk through your component requirements.