Choose the Right Plastic Material for Your Injection Molded Part
Picking the right plastic for your injection molded part matters. A lot.
Choose the right one, and the part runs for years.
Choose the wrong one, and it cracks, warps, or fails early.
We’ve seen both.
One customer once chose a lower-cost resin for a bracket near industrial equipment. On paper, it looked fine. In real use, heat built up. The bracket softened. The equipment shut down. Production stopped. The savings on resin disappeared fast.
Material choice is not about what is cheapest. It is about what works.
Let’s break it down.
Start With Where the Part Will Live
Before you look at resin names, look at the job.
Ask simple questions:
- Is it indoors or outside?
- Will it see heat?
- Does it carry weight?
- Will it touch chemicals?
- Does it need to insulate electricity?
The environment decides the material. Not the other way around.
A part inside a control panel has different needs than one mounted next to heavy equipment. Write down the real conditions. Use those facts to guide you.
Thermoplastic or Thermoset?
Most injection molded parts fall into one of two groups.
Thermoplastics
These melt when heated and harden when cooled. You can repeat that process.
They are common. Flexible. Good for high production runs.
Examples include:
- ABS
- Polypropylene
- Nylon
- Polycarbonate
They work well for housings, covers, brackets, and general industrial parts.
But they have limits. Some will soften under steady heat. Some will creep under long-term load.
Thermosets
Thermosets cure once. After that, they do not melt again.
They form a rigid structure. That structure handles heat and stress better.
Common types include:
- Phenolic
- Epoxy-based compounds
These are often used in electrical components and high-heat industrial settings.
If heat is high or loads are heavy, thermosets are often the better fit.
Focus on the Basics
You do not need to memorize every resin on the market. Focus on what matters.
Strength
Will the part hold weight? Take impact?
Nylon offers good strength. Reinforced materials offer even more. Thermosets provide high rigidity for tough conditions.
Heat
Know your operating temperature.
Moderate heat might be fine for polypropylene. Higher heat calls for engineered plastics or thermosets.
Heat breaks weak material. Do not guess here.
Chemicals
Oil. Cleaners. Solvents.
Some plastics resist chemicals well. Others swell or crack.
If your part sits in a harsh environment, check compatibility charts. Test if needed.
UV Exposure
Outdoor parts need UV protection. Without it, plastic can turn brittle.
If the part lives outside, say so early in the design process.
Cost Is Not Just the Price Per Pound
It is easy to focus on material cost.
But think bigger.
What does failure cost?
Downtime?
Replacement labor?
Lost production?
A slightly higher-grade resin can prevent larger losses later.
That does not mean overbuilding every part. It means matching the material to the job.
Volume Matters
If you are making thousands of parts, cycle time and consistency matter.
If you are producing specialized industrial components in moderate volume, durability may matter more.
Material affects mold design. Shrink rates. Cooling time. All of it connects.
That is why material selection should never happen in isolation.
Talk to Your Molder Early
Do not finalize your design before talking to your molding partner.
Material affects wall thickness. Tooling. Processing conditions.
We often review a part and suggest a small change. A rib adjustment. A material shift. A thickness tweak.
Those small changes can improve strength and lower production cost at the same time.
Changes are easy before tooling is cut. They are expensive after.
Quick Answers to Common Questions
What is the strongest plastic?
It depends on the job. Reinforced thermoplastics and thermosets handle heavy loads well.
What works best in high heat?
Thermosets often perform better under sustained high temperatures.
Can molded parts be used outdoors?
Yes. Just make sure UV resistance is built into the material.
Is the most expensive resin the best?
No. The best resin is the one that meets your real-world requirements.
Choosing the right plastic material for your injection molded part is about matching the resin to the job.
Define the environment.
Know the loads.
Understand the heat.
Plan for chemicals.
Make the decision based on facts, not assumptions.
If you are unsure, get input early. A short conversation during design can prevent major issues later.