Injection Molding Materials Guide
Find the right resin for your molded parts
Injection molding material selection impacts everything — cycle time, mold design, part strength, appearance, and cost. With thousands of resin grades available, this guide focuses on the most commonly specified materials and when to choose each.
Key Selection Factors
Melt Flow Index
How easily the plastic flows into thin walls and complex features.
Shrinkage Rate
How much the part shrinks during cooling — drives mold dimensional compensation.
Heat Resistance
Maximum continuous use temperature and heat deflection temperature (HDT).
Impact Resistance
How well the material resists breaking under sudden loads or drops.
Surface Appearance
Gloss, texture capability, colorability, and weld line visibility.
Chemical Resistance
Exposure to oils, solvents, cleaning agents, and UV light.
Recommended Materials
The most versatile injection molding plastic. Good strength, excellent surface finish, easy to paint/plate, and very forgiving in the molding process. The default choice for consumer products.
Optically clear, incredibly impact-resistant (250× stronger than glass), and stable up to 130°C. The material behind safety glasses, phone cases, and medical devices.
Cheapest engineering-grade plastic. Excellent chemical resistance, living hinge capability, and FDA food contact compliance. Low density means lighter parts.
The strongest common injection molding plastic. Glass-filled variants rival metals for structural applications. Absorbs moisture (factor into dimensional planning).
Best plastic for precision mechanical parts. Extremely low friction, excellent dimensional stability, and creep resistance. The go-to for gears, bearings, and mechanisms.
The apex predator of injection molding plastics. 250°C continuous use, chemically inert, FDA/biocompatible. 10–20× the cost of standard resins — use only when nothing else works.
💡 Pro Tips
- ▸ ABS is the safe default for consumer products. Start there unless you have a specific reason not to.
- ▸ PC/ABS blends give you the best of both worlds — PC's strength with ABS's processability.
- ▸ Glass-filled nylon (PA66 GF30) can replace die-cast aluminum at a fraction of the weight and cost.
- ▸ Shrinkage rates vary dramatically: PP shrinks 1.5–2.5% vs PC at 0.5–0.7%. This affects mold design.
- ▸ For food-contact applications, PP and specific PE grades are your best options — they're inherently FDA-compliant.
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