Top Plastics for High-Quality Injection Molding

Choosing the right plastic is one of the most critical decisions in any injection molding project. This choice dictates a part's mechanical strength, chemical resistance, finish, and final cost. With hundreds of commodity and engineering plastics available, making an informed decision based on your project's specific application is fundamental to its success. This guide provides a detailed look at the most common thermoplastic materials, their unique properties, and the key factors to consider for optimal results. With expertise in Design for Injection Molding (DfIM) and access to ISO-Certified Manufacturing, Aprios is equipped to help you choose materials that balance quality, compliance, and manufacturability.

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A Deeper Dive into Common Injection Molding Plastics

Each plastic possesses a unique profile of strengths and weaknesses. Understanding these nuances is key to matching a material to your part's intended function. The right choice supports plastic part design optimization, tooling solutions, and effective downstream processing, like secondary manufacturing processes.

Polypropylene (PP)

Polypropylene is a versatile and cost-effective commodity plastic. As one of the most widely used materials, it offers a great balance of mechanical and chemical properties.

• Key Properties: High fatigue resistance, excellent chemical resistance (acids, bases), and a high melting point.
  
• Common Applications: Automotive components (bumpers, interior trim), living hinges, medical-grade containers, and consumer product packaging.
  
• Considerations: Can be difficult to bond or paint, and has poor UV resistance without specific additives. Aprios often leverages PP in custom injection molding solutions for flexible, high-volume components.
  

Acrylonitrile Butadiene Styrene (ABS)

ABS is a popular engineering thermoplastic known for its toughness and aesthetic finish. It provides a good middle ground between standard plastics and high-performance engineering resins.

• Key Properties: High impact strength, good stiffness, and scratch resistance. It can also be easily colored and processed to achieve a high-gloss finish.
• Common Applications: Electronic housings (keyboards, printer casings), automotive dashboards, LEGO bricks, and protective headgear.
• Considerations: It has poor resistance to UV light (can become brittle and yellow outdoors) and is susceptible to attack by certain solvents. ABS is frequently chosen for plastic injection molding services requiring cosmetic appeal.

Polycarbonate (PC)

When exceptional toughness and transparency are required, Polycarbonate is a top choice. This incredibly durable engineering plastic can withstand significant impacts without fracturing.

• Key Properties: Outstanding impact strength, high stiffness, and impressive optical clarity. It also maintains its properties over a wide range of temperatures.
• Common Applications: Safety glasses, medical device components, automotive lighting, bullet-resistant "glass," and reusable water bottles.
• Considerations: It is prone to scratching without a hard coat and can be susceptible to stress cracking when exposed to certain chemicals. PC is compatible with Carbon DLS Prototyping and other additive manufacturing solutions used in functional testing.

Nylon (PA6 and PA66)

Nylon (Polyamide) is a family of engineering plastics prized for its exceptional mechanical strength, wear resistance, and low-friction properties.

• Key Properties: High tensile strength, resistance to abrasion and chemicals, and a high-temperature threshold.
• Common Applications: Gears, bearings, bushings, fasteners, and components in engine compartments that experience high friction and heat.
• Considerations: Nylon is hygroscopic, meaning it absorbs moisture from the environment, which can affect its dimensional stability and mechanical properties. PA66 is generally more dimensionally stable than PA6. It's ideal for injection mold design services where friction and load-bearing performance are essential.

High-Density Polyethylene (HDPE)

HDPE is a durable and highly versatile plastic known for its impressive chemical resistance and large strength-to-density ratio.

• Key Properties: Strong resistance to many solvents and chemicals, high impact strength even at low temperatures, and a waxy, low-friction surface.
• Common Applications: Chemical containers, cutting boards, milk jugs, and piping systems.
• Considerations: Has low stiffness compared to other plastics and is susceptible to stress cracking under certain conditions. It's frequently used in FDA-compliant manufacturing and medical injection molding due to its inertness.

Polyoxymethylene (POM / Acetal)

Often sold under brand names like Delrin®, POM is an engineering thermoplastic used for parts that require high stiffness, dimensional stability, and low friction.

• Key Properties: Significant rigidity and strength, low coefficient of friction, and very low moisture absorption.
• Common Applications: Precision gears, conveyor belt links, lock systems, and insulin pens.
• Considerations: Difficult to bond and has poor resistance to UV radiation and strong acids. Acetal is commonly selected for injection molding tooling or insert molding for medical devices requiring tight tolerances.

Polymethyl Methacrylate (PMMA / Acrylic)

Acrylic is a rigid thermoplastic valued for its superior optical clarity, weatherability, and scratch resistance, often used as a lightweight and shatter-resistant alternative to glass.

• Key Properties: Highest optical clarity of any plastic, remarkable UV stability (resists yellowing), and good scratch resistance.
• Common Applications: Light pipes, lenses for taillights, retail displays, and medical fluidics.
• Considerations: More brittle and has lower impact strength than Polycarbonate. PMMA works well in 3D printed prototypes and low-load environments requiring visibility.

Quick Comparison: Injection Molding Material Properties

Key Factors for Material Selection

Choosing the right material requires a careful analysis of your project's demands. Consider these factors:

• Mechanical Requirements: What forces will the part endure? Evaluate needs for tensile strength (pulling), impact resistance (sudden force), and fatigue resistance (repeated stress). Materials like PC and Nylon are excellent for high-stress applications, while PP offers great fatigue resistance for parts like living hinges.
• Environmental Exposure: Will the part be used outdoors or exposed to chemicals? For outdoor applications, PMMA or a UV-stabilized grade of another plastic is vital. For chemical exposure, HDPE and PP offer robust resistance.
• Temperature Range: What is the part's operating temperature? Materials like Nylon and PC maintain their integrity at higher temperatures, while some grades of HDPE perform well in colder environments.
• Aesthetic and Optical Needs: Is the part's appearance important? If you need transparency, PC and PMMA are the obvious choices. For a high-gloss, premium finish, ABS is a strong contender.
• Regulatory Compliance: Does the part need to meet standards like FDA for food contact or RoHS for electronics? Many materials are available in special grades that meet these requirements, so it's a critical factor to specify. For medical projects, Aprios provides ISO 13485 injection molding and DFM development services to ensure your design meets industry standards.

Partner with Aprios to Navigate Your Material Choices

The trade-offs between cost, strength, and processability can be complex. The team at Aprios has the expertise to guide you through the material selection process. We work with you to analyze your design and application, recommending the ideal plastic that delivers on performance and stays within budget. From initial prototype to full-scale production, we help get your project right from the start with design for manufacturing services, rapid prototyping services, and additive manufacturing for production.

Selecting the right plastic material is a foundational step for successful injection molding. By carefully considering the properties of each material against the demands of your application, you can produce a high-quality, durable, and cost-effective part. If you’re ready to discuss material options for your next project, contact the experts at Aprios today.

You can also view our Material Selection tool.