Material selection is a critical aspect of the plastic injection molding process, as it directly impacts the performance, durability, and overall success of the final plastic parts. With a wide range of plastic resins available, choosing the right material requires careful consideration of various factors. In this comprehensive guide, we will walk you through the process of material selection in custom injection molding, providing insights into the different types of resins, their properties, and the key factors to consider when choosing the optimal material for your project.

Understanding Plastic Resins

Plastic resins, also known as polymers, are the base materials used in plastic injection molding. Each resin has its unique set of properties, such as strength, flexibility, heat resistance, chemical resistance, and aesthetics. The choice of resin depends on the specific requirements of the part, including its intended application, operating conditions, and regulatory compliance.

Common Types of Plastic Resins

  1. Polyethylene (PE): PE is a versatile resin known for its excellent chemical resistance, low cost, and easy processability. It is commonly used for applications such as packaging, containers, and automotive components.
  2. Polypropylene (PP): PP offers high impact strength, chemical resistance, and good dimensional stability. It is widely used in automotive parts, appliances, and packaging due to its lightweight nature and cost-effectiveness.
  3. Acrylonitrile Butadiene Styrene (ABS): ABS resin provides a balance of strength, impact resistance, and surface finish. It is commonly used in consumer electronics, automotive interior parts, and toys.
  4. Polycarbonate (PC): PC is a transparent resin known for its exceptional impact resistance and high heat resistance. It is often used in applications that require optical clarity, such as automotive lenses, safety goggles, and electronic display panels.
  5. Polyamide (PA or Nylon): PA offers high strength, toughness, and resistance to wear and abrasion. It is commonly used in applications such as gears, bearings, and electrical connectors.
  6. Polyethylene Terephthalate (PET): PET is a strong and lightweight resin known for its excellent barrier properties against moisture and gases. It is widely used in the packaging industry for bottles, containers, and food packaging.

Key Factors to Consider

When selecting the right resin for your mold manufacturing project, several factors come into play:

  1. Mechanical Properties: Evaluate the required mechanical properties of the part, such as strength, stiffness, and impact resistance. Consider factors such as load-bearing capacity, temperature range, and anticipated stresses the part will experience during its lifespan.
  2. Chemical Compatibility: Determine the chemical resistance requirements of the part. Consider the exposure to chemicals, solvents, oils, and other substances the part may encounter in its intended application.
  3. Environmental Factors: Consider the environmental conditions the part will be exposed to, such as temperature extremes, UV radiation, moisture, and humidity. Choose a resin that can withstand these conditions without compromising its performance.
  4. Regulatory Compliance: Ensure that the chosen resin meets the necessary regulatory requirements and certifications for your industry. This may include considerations such as food contact safety, flame resistance, or electrical conductivity.
  5. Aesthetics and Surface Finish: Consider the desired appearance and surface finish of the part. Certain resins offer better aesthetics, such as high-gloss finishes or transparent properties, which may be crucial for specific applications.
  6. Cost Considerations: Assess the cost implications of the chosen resin, including material cost, processing costs, and potential recycling or waste management considerations. Balancing cost-effectiveness with performance is essential.

Collaboration with Material Suppliers

Engaging in collaboration with material suppliers and resin manufacturers can provide valuable insights into material selection. They can offer technical expertise, provide data sheets, and assist with material testing and validation. Their knowledge of the latest advancements in resin technology and their understanding of industry-specific requirements can help guide your material selection process.

Testing and Validation

Before proceeding with full-scale production, it is essential to conduct testing and validation of the chosen resin. This can include prototyping, functional testing, and performance analysis to ensure that the selected material meets the desired specifications and performance expectations.


Material selection is a crucial step in the plastic injection molding process, as it directly impacts the functionality, durability, and overall success of the final plastic parts. By considering factors such as mechanical properties, chemical compatibility, environmental factors, regulatory compliance, aesthetics, and cost, you can make an informed decision when choosing the optimal resin for your project. Collaboration with material suppliers and conducting testing and validation further ensures the suitability of the selected resin. With careful material selection, you can achieve the desired performance and quality in your plastic injection molding project.