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How to Choose the Right Material for Injection Molding

Choosing the right material for injection molding is crucial for the success of any manufacturing project. The material used can greatly impact the quality, durability, and cost-effectiveness of the final product. Understanding the key factors involved in material selection is essential for making informed decisions in the injection molding process.

Key Takeaways

  • Consider the strength and durability of the material for the intended application.

  • Evaluate the heat resistance of the material to ensure it can withstand the production environment.

  • Take into account the chemical resistance of the material to avoid degradation over time.

  • Consider cost considerations such as material expenses and production volume.

  • Ensure that the material selected meets the design requirements and specifications for the intended product.

Understanding Injection Molding Materials

Key Factors to Consider

When considering the key factors for injection molding materials, it's essential to evaluate the plasticization process and the injection process. The plastic material is melted at high temperatures in the material tube, and then the injection process involves the use of a screw to inject the molten material into the mold. These processes are critical in determining the quality and characteristics of the final molded product. Additionally, the material's flowability and viscosity play a significant role in the injection molding process, affecting the overall efficiency and outcome of the production.

Material Selection Process

When it comes to the material selection process, it is crucial to consider a thorough understanding of the desired product attributes. This includes the physical, mechanical, and thermal characteristics of the material. Additionally, cost considerations, design requirements, and production volume play a significant role in the decision-making process. Implementing a table for presenting structured, quantitative data can be beneficial in comparing different materials. A bulleted list can also be used to highlight the key factors to consider during the material selection process. Remember, a thorough understanding helps select a material that aligns with the desired product attributes.

Types of Injection Molding Materials


Thermoplastics are a popular choice for injection molding due to their versatility and ease of recycling. They can be molded and remolded multiple times, making them a cost-effective option for high-volume production. Additionally, thermoplastics exhibit excellent impact resistance and chemical resistance, making them suitable for a wide range of applications. When considering thermoplastics for injection molding, it's important to evaluate their specific properties and performance characteristics.


Thermosets are a type of material used in injection molding that undergoes a chemical reaction to harden. Unlike thermoplastics, thermosets are irreversibly formed and are known for their exceptional strength and durability. They are usually stronger than other materials and are ideal for applications requiring high heat resistance.


Elastomers, often known as rubbery materials, are a unique category of injection molding materials that combine flexibility with resilience. Unlike thermoplastics and thermosets, elastomers can undergo significant deformation and still return to their original shape without permanent deformation. This makes them ideal for products that require a high degree of flexibility, such as seals, gaskets, and various flexible connectors.

Elastomers come in various types, with Thermoplastic Elastomers (TPE) being particularly noteworthy. TPEs offer the combined benefits of plastic and rubber, providing both the elastic properties of elastomers and the recyclability of thermoplastics. They can be easily processed by standard techniques such as injection molding when heated, and they do not require curing or vulcanization, which can save on production time and costs.

Common Elastomers Used in Injection Molding:

  • Natural Rubber (NR)

  • Silicone Rubber (SiR)

  • Nitrile Rubber (NBR)

  • Butyl Rubber (IIR)

Each of these elastomers has its own set of properties that make it suitable for specific applications. It is crucial to match the material characteristics with the product's intended use to ensure optimal performance.

Properties of Ideal Injection Molding Materials

Strength and Durability

When selecting materials for injection molding, strength and durability are paramount. These properties ensure that the final product can withstand the intended use without failure. Materials with high tensile strength are capable of resisting stretching or pulling forces, making them ideal for parts that will be under constant stress or load.

Plastic injection molded parts vary in strength, but they typically exhibit tensile strengths ranging from 3,500 to 10,000 psi. This range allows for a wide selection of materials to match the specific strength requirements of different applications. For instance, materials with higher tensile strength are chosen for components that need to bear heavy loads or resist impact.

Heat Resistance

When selecting materials for injection molding, heat resistance is a critical property to consider. Materials must be able to withstand the high temperatures involved in the molding process without degrading or losing their mechanical properties. Some materials are specifically formulated to enhance their ability to resist heat.

For example, certain grades of plastics are designed to maintain structural integrity at elevated temperatures. Below is a table illustrating the heat deformation temperatures of common injection molding materials:

Note: The actual heat resistance will vary based on the material's formulation and the processing conditions.

Chemical Resistance

When it comes to choosing the right material for injection molding, chemical resistance is a crucial factor to consider. The material's ability to withstand exposure to various chemicals and solvents can significantly impact the performance and longevity of the molded parts. In addition to chemical resistance, heat resistance and strength and durability are also key properties to evaluate in an ideal injection molding material. Here's a brief overview of these properties:

  1. Strength and Durability: The material should exhibit high tensile strength and toughness to withstand mechanical stress and impact.

  2. Heat Resistance: The material should have the ability to maintain its structural integrity and dimensional stability at elevated temperatures.

  3. Chemical Resistance: As mentioned earlier, the material should resist degradation and damage when exposed to chemicals and solvents.

Considering these properties is essential for selecting the most suitable material for injection molding.

Factors Affecting Material Selection

Cost Considerations

When selecting materials for injection molding, cost is a critical factor that can significantly impact the overall budget of a project. The price of materials can vary widely, with some plastics costing as little as $1 per kg and others as much as $5 per kg. It's essential to balance the cost with the performance requirements of the final product.

  • Material costs are not the only expense to consider; processing, labor, and tooling costs also contribute to the final cost. A comprehensive cost analysis should include:

  • Raw material expenses

  • Processing and labor costs

  • Tooling and setup charges

  • Maintenance and operational costs

Design Requirements

When considering the design requirements for injection molding materials, it is important to focus on the specific needs of the product. Factors such as dimensional accuracy, surface finish, and mechanical properties play a crucial role in material selection. Additionally, the compatibility of the material with the design features and the manufacturing process should be carefully evaluated. It is also essential to consider the impact resistance and environmental factors that the product will be exposed to during its lifecycle. These considerations will ensure the successful integration of the chosen material with the design requirements.

Production Volume

When considering the production volume for an injection molding project, it's important to evaluate the scalability of the chosen material. High production volumes may benefit from materials that offer cost efficiency and fast cycle times. On the other hand, low production volumes may allow for more flexibility in material selection, prioritizing specific material properties over production cost. It's crucial to strike a balance between material cost and performance to optimize the overall production process.


In conclusion, selecting the right material for injection molding is a critical decision that can significantly impact the quality and performance of the final product. It is important to consider factors such as cost, durability, and manufacturability when making this choice. By carefully evaluating these aspects and understanding the specific requirements of the project, manufacturers can ensure the successful production of high-quality injection-molded parts.

Frequently Asked Questions

What are the key factors to consider when choosing injection molding materials?

The key factors to consider include mechanical properties, chemical resistance, heat resistance, cost, and design requirements.

What are the types of injection molding materials commonly used?

Common types of injection molding materials include thermoplastics, thermosets, and elastomers.

What are the properties of ideal injection molding materials?

Ideal injection molding materials exhibit high strength and durability, excellent heat resistance, and strong chemical resistance.

How do cost considerations affect material selection for injection molding?

Cost considerations impact material selection by influencing the overall production cost and the affordability of the chosen material.

What design requirements should be considered when selecting injection molding materials?

Design requirements such as part geometry, surface finish, and dimensional accuracy play a crucial role in material selection for injection molding.

How does production volume affect the choice of injection molding materials?

Production volume affects material selection by influencing the overall cost per part and the feasibility of using certain materials for high-volume production.

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