Injection Molding Material Selection: Complete Guide for Engineers

Injection molding is one of the most popular manufacturing processes for plastic parts—but its success lives or dies by injection molding material selection. Pick the wrong material, and your part might crack under stress, melt in high temperatures, or fail to meet industry standards. Pick the right one, and you’ll get durable, cost-effective parts that fit your project’s needs perfectly. This guide breaks down how to choose injection molding materials, key material options (with their strengths and uses), real-world case studies, and a step-by-step selection process to avoid mistakes.

Why Injection Molding Material Selection Matters (Cost, Quality, Safety)

Choosing an injection molding material isn’t just about picking a plastic—it’s about aligning the material’s properties with your part’s purpose. A bad choice can lead to three big problems:

1. Increased Costs: If a material is too weak (e.g., using PLA for a load-bearing bracket), you’ll have to rework or replace parts—wasting time and money.
2. Quality Failures: A material that can’t handle its environment (e.g., using LDPE for a high-temperature engine part) will crack, warp, or degrade quickly.
3. Safety Risks: For medical or food-contact parts, using non-certified materials (e.g., non-food-grade PVC) can cause contamination or harm.

Example: A toy company once used low-quality ABS (not impact-resistant) for children’s building blocks. The blocks broke easily, leading to a recall that cost $200,000. Switching to high-impact ABS fixed the issue—proving how critical material selection is.

Key Factors to Consider When Choosing Injection Molding Materials

Before diving into specific materials, you need to answer 5 core questions—these will narrow down your options and ensure you pick a material that works for your project.

1. Mechanical Requirements (Strength, Flexibility, Durability)

Your part’s job determines the mechanical properties it needs. For example:

• A load-bearing bracket needs high tensile strength (to resist pulling forces).
• A phone case needs impact resistance (to survive drops).
• A gasket needs flexibility (to seal tightly).

Tip: If your part needs multiple properties (e.g., strength + flexibility), look for blends like PC-ABS (combines PC’s strength with ABS’s impact resistance).

2. Environmental Conditions (Temperature, Chemicals, Weather)

Where will your part be used? A part in a car engine needs to handle heat, while a part in a cleaning product needs to resist chemicals.

3. Aesthetic Needs (Color, Transparency, Finish)

Does your part need to look good? Transparent parts (e.g., water bottles) need clear materials, while branded parts need consistent color.

4. Cost (Material Price + Processing Costs)

Materials vary widely in price—from cheap LDPE (\(1–\)2 per kg) to expensive PEEK (\(80–\)100 per kg). But don’t just look at material cost: processing costs matter too.

• Easy-to-process materials (e.g., ABS, PP) have lower molding costs (faster cycle times, less tool wear).
• Hard-to-process materials (e.g., PEEK, PEI) need higher temperatures and specialized tools—adding to costs.

5. Regulatory Compliance (Certifications for Safety)

Certain industries have strict rules about materials. For example:

• Food-contact parts: Need FDA or EU 10/2011 certification (materials like HDPE, PP qualify).
• Medical parts: Need biocompatibility certification (ISO 10993) (materials like PLA, PEEK qualify).
• Automotive parts: Need flame-retardant or heat-resistant certifications (materials like PPS, PC-ABS qualify).

Warning: Never use non-certified materials for regulated parts—this can lead to fines or product recalls.

Top Injection Molding Materials (Properties, Uses, Case Studies)

Below are the most common injection molding materials, with their key properties, best uses, and real-world examples. We’ve organized them by category to make selection easier.

1. General-Purpose Plastics (Low Cost, Versatile)

These materials are cheap, easy to process, and work for simple parts that don’t need extreme properties.

ABS (Acrylonitrile Butadiene Styrene)

• Key Properties: High impact resistance, tough, scratch-resistant, low melting point (180–230°C).
• Best Uses: Consumer goods (phone cases, toys), automotive parts (glove boxes), electronics (keyboards).
• Case Study: A electronics brand used ABS to make 100,000 keyboard frames. ABS’s impact resistance prevented cracks during shipping, and its easy dyeing let the brand offer 5 colors. The total cost was $3 per frame—half the cost of using PC.

HDPE (High-Density Polyethylene)

• Key Properties: Lightweight, chemical-resistant, water-impermeable, food-grade.
• Best Uses: Food containers (milk jugs), pipes, medical devices (syringe barrels).
• Case Study: A dairy company used HDPE for 500,000 milk jugs. HDPE’s chemical resistance kept milk fresh, and its food-grade certification met FDA standards. The jugs cost $0.50 each—cheaper than PET and more durable.

PP (Polypropylene)

• Key Properties: Moisture-resistant, flexible, impact-resistant, food-grade.
• Best Uses: Food containers (yogurt cups), packaging, automotive parts (bumpers), medical devices (face mask frames).
• Case Study: A medical supply company used PP for 1 million face mask frames. PP’s flexibility let the masks fit different face shapes, and its moisture resistance prevented degradation from sweat. The frames cost $0.10 each—affordable for high-volume production.

2. Engineering Plastics (High Performance, Durable)

These materials have better mechanical or environmental properties than general-purpose plastics—ideal for demanding applications.

PC (Polycarbonate)

• Key Properties: Transparent, high impact resistance, heat-resistant (up to 130°C), strong.
• Best Uses: Eyeglass lenses, water bottles, automotive parts (headlight covers), electronics (laptop casings).
• Case Study: A laptop brand used PC for 200,000 laptop casings. PC’s transparency let the brand add LED lights, and its impact resistance survived drops from 1 meter. The casings cost $4 each—more than ABS but worth it for durability.

PA 66 (Nylon 66)

• Key Properties: Rigid, wear-resistant, high melting point (250–260°C), resistant to hydrocarbons.
• Best Uses: Moving parts (gears, bearings), automotive parts (fuel lines), industrial components (valves).
• Case Study: An automotive supplier used PA 66 for 50,000 gear parts. PA 66’s wear resistance let the gears last 100,000 miles (twice as long as ABS gears), and its hydrocarbon resistance handled engine oil. The gears cost $2 each—justified by longer lifespan.

PC-ABS Blend

• Key Properties: Combines PC’s strength/heat resistance with ABS’s impact resistance/ease of processing.
• Best Uses: Automotive parts (dashboard panels), electronics (TV frames), consumer goods (power tool casings).
• Case Study: A power tool brand used PC-ABS for 100,000 drill casings. PC-ABS survived drops (impact resistance) and handled heat from the motor (heat resistance). The casings cost $3.50 each—cheaper than pure PC and more durable than pure ABS.

3. High-Performance Plastics (Extreme Conditions)

These materials handle extreme heat, chemicals, or stress—used for aerospace, medical, or industrial applications.

PEEK (Polyether Ether Ketone)

• Key Properties: High heat resistance (up to 250°C), chemical-resistant, biocompatible, strong.
• Best Uses: Medical implants (spinal fusion parts), aerospace components (engine parts), industrial parts (high-temperature valves).
• Case Study: A medical device company used PEEK for 10,000 spinal implants. PEEK’s biocompatibility prevented rejection, and its strength matched bone density. The implants cost $50 each—expensive but critical for patient safety.

PEI (Polyetherimide)

• Key Properties: Heat-resistant (up to 190°C), flame-retardant, strong, low moisture absorption.
• Best Uses: Aerospace parts (wire insulation), automotive parts (temperature sensors), electronics (circuit boards).
• Case Study: An aerospace company used PEI for 5,000 wire insulation parts. PEI’s heat resistance handled engine temperatures, and its flame retardancy met safety standards. The parts cost $15 each—necessary for high-risk applications.

4. Flexible Plastics (Elastomers)

These materials are soft and elastic—ideal for seals, gaskets, or parts that need to bend.

TPE (Thermoplastic Elastomer)

• Key Properties: Flexible, tear-resistant, abrasion-resistant, easy to process.
• Best Uses: Seals (water bottle lids), grips (tool handles), toys (soft edges).
• Case Study: A tool brand used TPE for 200,000 tool grips. TPE’s flexibility made the grips comfortable to hold, and its abrasion resistance prevented wear. The grips cost $0.80 each—cheaper than rubber and easier to mold.

TPV (Thermoplastic Vulcanizate)

• Key Properties: Durable, solvent-resistant, weather-resistant, lightweight.
• Best Uses: Automotive parts (gaskets, shock absorbers), consumer goods (shoe soles), industrial parts (hose seals).
• Case Study: A car manufacturer used TPV for 500,000 door gaskets. TPV’s weather resistance prevented cracking from sun/rain, and its solvent resistance handled cleaning chemicals. The gaskets cost $1 each—lasted twice as long as rubber gaskets.

Step-by-Step Injection Molding Material Selection Process

Follow these 4 steps to pick the perfect material—no guesswork needed.

Step 1: List Your Part’s Non-Negotiable Requirements

Start by writing down the must-have properties:

• Example: “Food-grade, transparent, impact-resistant, cost under $3 per kg.”

Step 2: Filter Materials by Requirements

Use the tables above to narrow down options. For the example above, possible materials are HDPE (food-grade, but not transparent) or PC (transparent, impact-resistant, but cost \(4–\)6 per kg) or PET (food-grade, transparent, cost \(3–\)5 per kg).

Step 3: Test Prototypes with 2–3 Top Materials

Never skip prototyping! Make small batches (10–20 parts) with your top materials and test them:

• For food parts: Check if they meet FDA standards.
• For impact-resistant parts: Drop-test them to see if they break.

Example: A water bottle brand tested PET and PC prototypes. PET was cheaper (\(3 per kg vs. \)5 for PC) and met FDA standards—so they chose PET.

Step 4: Finalize and Validate

Once you pick a material, confirm:

• It meets all regulatory requirements.
• The total cost (material + processing) fits your budget.
• The material is available in the color/grade you need.

Yigu Technology’s Perspective on Injection Molding Material Selection

At Yigu Technology, we help clients cut through the noise of injection molding material selection. We start by understanding their part’s purpose—whether it’s a food container or an aerospace component—then match it to materials that balance performance and cost. For general parts, we recommend ABS or PP for affordability; for high-performance needs, PEEK or PC-ABS. We also offer prototype testing to validate materials before full production, avoiding costly mistakes. Our team shares material specs (like HDPE’s chemical resistance or TPE’s flexibility) upfront, so clients make informed choices. For us, the right material isn’t just about properties—it’s about making your part work, last, and fit your budget.

FAQ About Injection Molding Material Selection

1. What’s the cheapest injection molding material for high-volume parts?

LDPE (Low-Density Polyethylene) is the cheapest—costing \(1–\)2 per kg. It’s easy to process and works for simple parts like plastic bags, toys, or basic containers. For parts that need more strength (e.g., food containers), HDPE (\(1–\)2 per kg) is a better cheap option.

2. Can I use the same material for both injection molding and 3D printing?

Some materials work for both—like ABS, PLA, or PET. But injection molding grades are often different (e.g., injection molding ABS has higher melt flow for easier molding). Using 3D printing filament for injection molding can lead to poor part quality (e.g., warping). Always use material grades specifically designed for injection molding.

3. What material should I use for medical injection molding parts?

Use biocompatible, ISO 10993-certified materials. Top choices include:

• PLA (biodegradable, good for temporary implants like sutures).
• PEEK (strong, heat-resistant, good for permanent implants like spinal parts).
• HDPE (food-grade, good for medical devices like syringe barrels).

Always confirm the material has the right certifications before use.