Choosing the right plastic for injection molding isn’t just about picking what’s cheapest or most available.
It’s about choosing a material that matches your part’s function, performance, and cost requirements.
In this guide, you’ll learn how to choose the right plastic materials for your injection molding parts.
6 Steps to Choose the Right Plastic for Injection Molding
Step 1: Define Your Part’s Requirements
Before picking a plastic, get clarity on what your part needs to do.
| Category | Key Questions |
|---|---|
| Mechanical | Does it need to handle impact, bending, or load-bearing? |
| Thermal | Will it be exposed to high temperatures or thermal cycling? |
| Chemical | Will it contact oils, solvents, cleaners, or acids? |
| Environmental | Is it for outdoor use? UV exposure? Moisture? |
| Aesthetic | What color, texture, or transparency is required? |
| Regulatory | Any FDA, RoHS, or ISO standards it must meet? |
| Production Volume | High-volume or low-volume? Will you amortize tooling cost? |
Don’t choose plastic just because it worked in a past project — every design has different constraints.
Step 2: Understand the Main Plastic Families
There are hundreds of polymers on the market. But most fall into these main categories:
Thermoplastics vs. Thermosets
- Thermoplastics: Melt and re-solidify. Ideal for injection molding. Recyclable.
- Thermosets: Irreversibly hardened. Used less often in molding.
This guide focuses on thermoplastics, the dominant material class for injection molding.
Step 3: Compare Common Injection Molding Plastics
Here’s a quick overview of widely used plastics — and how they compare.
| Material | Pros | Cons | Typical Uses |
|---|---|---|---|
| ABS | Tough, easy to mold, good surface finish | Not UV or chemical resistant | Consumer goods, enclosures, toys |
| Polypropylene (PP) | Chemically resistant, flexible, low cost | Warps under heat, poor bonding | Caps, containers, living hinges |
| Polycarbonate (PC) | High strength, impact resistant, transparent | Expensive, scratches easily | Safety lenses, electronics, guards |
| Nylon (PA) | Strong, abrasion-resistant, self-lubricating | Absorbs moisture, shrinks | Gears, bearings, automotive |
| POM (Acetal) | Low friction, dimensionally stable | Poor UV resistance, flammable | Gears, mechanical parts, bushings |
| PEEK | High-temp, chemical resistant, wear resistant | Very expensive, difficult to mold | Aerospace, medical, oil & gas |
| HDPE/LDPE | Flexible, chemical resistant, cheap | Low stiffness, poor dimensional accuracy | Bottles, containers, disposable products |
Note: This is not exhaustive. Specialty additives and blends exist for flame retardancy, antistatic properties, bio-compatibility, and more.
Step 4: Match Material to Function
Let’s make it easier: match materials to the most common use-case priorities.
| Requirement | Best Materials |
|---|---|
| High impact resistance | Polycarbonate, ABS |
| Chemical resistance | PP, PEEK, HDPE |
| Wear resistance | Nylon, Acetal, PEEK |
| Low cost | PP, PE, PS |
| High stiffness | Glass-filled Nylon, PC, PEEK |
| UV resistance | UV-stabilized ABS, ASA, PC blends |
| Transparency | PC, PETG, Acrylic |
| High temperature | PEEK, PPS, Polyimide |
| Living hinge / Flexing | PP, HDPE |
| Food contact | PP, HDPE, PET, specific FDA-grade resins |
Every material is a trade-off. Don’t expect “perfect” — aim for “best fit.”
Step 5: Consider Processing and Cost Impacts
The plastic you choose affects not just performance — but manufacturing feasibility.
| Factor | Impact of Plastic Choice |
|---|---|
| Mold design complexity | High-flow plastics like PP are easier to mold |
| Shrinkage rate | Materials like nylon shrink more than PC |
| Cycle time | Faster-cooling materials reduce unit cost |
| Tool wear | Glass-filled or abrasive materials wear molds |
| MOQ and sourcing | Commodity plastics are easier to procure globally |
A good material that’s hard to mold is still a bad decision.
Step 6: Ask Your Molder
Still unsure? Ask your injection molding partner.
They’ll have experience with:
- Material substitution strategies
- Processing challenges for each resin
- Mold flow simulation data
- Sourcing options and lead time trade-offs
👉 Request a DFM (Design for Manufacturability) review — it often reveals material-specific improvements before tooling begins.
Final Thoughts
Choosing the right plastic isn’t guesswork. It’s a structured decision based on function, environment, cost, and processing.
Here’s a quick recap:
- Define your part’s mechanical, thermal, and regulatory needs
- Compare top plastics by performance and trade-offs
- Consider processing ease and total cost — not just raw resin price
- Get input from your molding partner or material supplier
The right plastic can save you time, cost, and headaches — while making your product more reliable.
Need help choosing or testing materials for your part? Contact RJC Mold.
