How to Choose the Best Plastic for Plastic Injection Molding?

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Aiming to produce thousands and thousands of plastic products? Injection molding has got you covered. Due to its high levels of accuracy, affordable unit costs, and short lead times, this process has massively revolutionized the plastic mass production industry. 

Injection molding basically involves injecting a molten polymer into a mold using both speed and precision then cooling it off quickly to form the desired part. With this method, you can create various products including consumer goods, automotive parts, aerospace components, medical equipment, among others. 

Nonetheless, the type of material you use plays a vital role in determining quality and performance of your end product as well as efficiency of your injection molding. Additionally, material determines temperature and pressure elements thus is a great cost factor. Keep reading to understand how to optimally select a plastic material fit for your plastic injection molding project. 

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Injection Molding Material (Image Source: Shutterstock)

Understanding Plastic Material Properties

Injection molding boasts a wide selection of materials, offering solutions that cater to various needs. From common plastics such as polypropylene to engineering-grade resins such as polycarbonate, the options are many.

Each material has unique properties, including strength, flexibility, resistance to heat and chemicals, and cost. More specialized materials, such as glass-filled nylon, offer enhanced properties, including higher tensile strength and rigidity. 

Manufacturers can customize many materials by using additives to enhance color, flame retardancy, or other specific attributes. With the myriad of choices available, it is paramount to have a solid understanding of each material and its properties. A thorough understanding of the materials allows you to make an informed decision that will yield a successful product.

Many polymers are somewhat crystalline, others are highly amorphous. Crystallinity defines the order/regularity of polymer chains. High crystallinity typically leads to greater stiffness, strength, and heat resistance. Lower crystallinity results in greater flexibility and transparency.

Crystalline regions in polymers are more organized and dense, affecting properties like melting point and tensile strength, while amorphous regions improve flexibility and impact resistance. Balancing these properties is essential in selecting a polymer for an application.

Reinforcing many polymers is achieved with addition of glass fibers. This can greatly enhance stiffness, strength and wear resistance. It can be detrimental to impact resistance, tool wear, abrasiveness and moisture absorption.

High-performance polymers with exceptional properties are required in demanding environments. They excel in chemical resistance, high-temperature stability and superior strength.

Common uses include; aerospace; automotive; medical and surgical instruments, implants; electronics; valves and seals. They ensure reliability and durability under extreme conditions.

Analyzing Application Requirements

A product’s functionality needs to meet the user’s goals and needs, and selecting the best material for the product assists in this endeavor. This functionality involves a detailed analysis of how to use your product and the various conditions it will experience.

For instance, a kitchen utensil that comes into contact with food and endures high temperatures requires a food-safe, heat-resistant plastic such as polypropylene. 

On the other hand, a protective helmet needs a material that offers high impact resistance, such as polycarbonate.

It’s also worth considering regulatory requirements that may apply to your product, ensuring the material used complies with all necessary standards. This careful alignment of product functionality and material properties optimizes your final product’s performance, safety, and longevity, leading to a successful injection molding project.

With the increasing environmental concerns, you shouldn’t also overlook the ecological impact of injection molding material selection. Determining the sustainability of a material involves considering its life cycle from extraction, production, and usage to eventual disposal.

Some materials, such as biodegradable plastics, minimize environmental harm as they break down naturally over time. Other materials are recyclable, reducing waste and the need for new raw materials. Incorporating sustainability into material selection enhances your company’s reputation for social responsibility. 

Considering Design Specifications

Part design plays an important role in material selection in plastic injection molding. Here are some properties that affect part design and influence material selection.

Wall Thickness

The thickness of the wall in plastic parts affects material selection. It is important to consider the viscosity, cooling time, and the structural integrity of the part. Thin walls need materials with good viscosity properties to ensure proper filling and packing during injection molding. On the other hand, thick walls may require the use of materials with higher strength so as to maintain structural integrity.

The Rib Design 

Ribs are the structural features added to a part to boost its strength and stiffness. certain materials are suited for accommodating rib geometry and provide sufficient reinforcement. Materials with high tensile strength and stiffness are preferred for rib designs.

Aesthetic Considerations 

Material selection for plastic parts considers factors such as color, texture, and the surface finishes of the part. Manufacturers should consider materials that meet their aesthetic requirements and should be compatible with post-processing techniques such as painting and printing.

The selection of plastics for accommodating complex designs depend on the requirements of the application such as mechanical properties and aesthetic considerations.

Evaluating Cost Implications

When choosing the best plastic for injection molding it is important to consider several cost factors. Here is an overview of some of these factors:

1. Raw Material Costs

This involves the costs incurred when purchasing the plastic material used in injection molding. The cost per unit weight varies depending on different types of plastic, influenced by factors such as material type and availability. High-performance plastics have higher prices due to their enhanced properties.

2. Processing Expenses

The processing expenses are costs associated with the injection molding process. This involves the equipment being used, labor, and energy. The cost of injection molding machines varies depending on the size, configuration, and automation features.

The labor cost involves the wages of machine operators and other personnel involved in the molding process. Energy costs include electricity and other utilities required to operate injection molding machines.

3. Lifecycle Cost 

This refers to all the costs associated with the product from the initial material procurement, production, usage, maintenance, and repairs. With high production volume, injection molding offers economies of scale resulting in an overall lower per unit cost in production. Factors such as durability, reliability, and recycling options contribute to lifecycle costs.

To balance material performance with budget constraints to achieve cost-effective manufacturing it is essential to first define the performance requirement of the product. Then prioritize key properties that are essential for the functionality and end use of the product. Another factor is material selection considering mechanical properties, durability, and cost.

Exploring Common Plastics Used in Injection Molding

There is a wide selection of injection molding materials to choose from. These materials exhibit different characteristics and have distinct use cases based on the pros and cons of each. 

1. Polyamide (Nylon)

Nylon is a highly flexible and ever-changing thermoplastic injection molding material and is useful for a wide range of applications. The reason for its utility in plastic injection is the fact that it performs wonderfully in mechanical and electrical systems. It has a considerable toughness threshold and a strong resistance to wear and tear.

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Nylon Injection Molding Material (Image Source: Shutterstock)

The product also has a strong chemical-resistant composition and is available at market-competitive prices. Nylon is ideal for industrial applications as all of these factors have to be considered to meet industry standards.

2. Acrylonitrile Butadiene Styrene (ABS)

ABS is strongly resistant to corrosive chemicals and to physical impacts. The material is pliable and is easy to use under a machine.

This injection molding material has a low melting point and as injection molding requires melting of the polymer, manufacturing products from the material require much less energy and effort. It is less expensive than its other counterparts and is not good for high heat utility.

3. High-Density Polyethylene (HDPE)

Polyethylene polymer is a thermoplastic polymer which means that it can be reheated to its melting point on multiple occasions. The reason this is a useful feature is that the plastic can be used for injection molding over and over again with no fear of waste.

This plastic is crystalline in texture, has a higher density than usual, and is used mainly in construction such as drain pipe manufacturing. One of the famous derivatives of polyethylene is the Ultrahigh Molecular Weight Polyethylene (UHMW) which is used in intense performance products such as bulletproof vests and medical devices.

4. Polycarbonate (PC)

This is a transparent and amorphous thermoplastic material that resembles glass in its capacity for the transmission of internal light. It is good for when the product requires transparency and also needs to be impact-resistant.

PC is used in the production of contact lenses, medical and automotive device parts, greenhouse, digital disks, exterior lighting fixtures, and many other similar applications due to its glass-like properties.

5. Polypropylene (PP)

The product has chemical resistance, elasticity, and fatigue resistance along with strong insulation and toughness properties. All of these characters combined, make the plastic an exceptionally high-quality polymer.

This is one of the most widely used plastics in the world and has a utility in the automotive industry, electrical and equipment industry, and construction industry.

6. Acrylonitrile Butadiene Styrene + Polycarbonate (ABS + PC) Blend

This injection molding thermoplastic is a combination of two different types of polymers. ABS has a high processing ability ratio and PC has a great array of mechanical properties along with impact and heat resistance.

As these two polymers come together, the final product is a polymer that offers high resistance, excellent impact resistance, and a good flow characteristic. PC+ABS offers combined properties of PC and ABS (high processing ability of ABS along with excellent mechanical properties and impact and the heat resistance of PC).

The ratio of the two components affects the heat resistance of the final product and the blend exhibits excellent flow characteristics. It is mainly used in a wide variety of industries such as in computer and business machinery, electrical applications, medical components, cellular phones, and home products such as lawn equipment. 

Sustainable and Eco-friendly Options

The growing importance of sustainability in material selection has driven a shift towards environment-friendly and socially responsible manufacturing processes. Sustainable material selection takes into consideration factors such as energy consumption, greenhouse gas emissions, resource depletion, and waste generation. By selecting materials with low environmental impact manufacturers can contribute to environment preservation. 

Sustainable material selection prioritizes the conservation of resources such as water and minerals. By adopting renewable materials manufacturers can reduce their dependence on these resources, overall reducing the environmental impact associated with resource mining and processing.

Another aim that is associated with sustainable material selection is the aim to minimize waste generation, and comply with regulations and consumer demands. There are guidelines and regulations that manufacturers are supposed to adhere to ensure environmental protection. Consumer preferences are shifting towards products that are made from sustainable materials.

Bioplastics and recycled materials offer eco-friendly alternatives for injection molding reducing environmental impact. Bioplastic is a biodegradable material that comes from renewable sources such as plants while recycled materials are sourced from post-consumer waste and processed into new materials.

Consulting with Material Suppliers and Experts

Collaborating with material suppliers and experts for material selection is crucial for making informed decisions in manufacturing. These suppliers and experts possess specialized knowledge and experience in various materials and their applications that you can utilize in your manufacturing.

They can offer guidance and recommendations on the most suitable materials for specific application-making considerations such as mechanical properties, thermal stability, and environmental factors. Material suppliers can provide samples for testing to evaluate the properties and performance under certain conditions. This ensures that the manufacturer asses factors such as strength and wear resistance ensuring the chosen material meets the desired specification.

Evaluating Your Injection Molding Suppliers and Experts

Knowledge and experience are baseline criteria for consideration of a custom injection molder for complex applications. What differentiates suppliers/experts with true partnership potential, though, is diversity: 

1. Market Versatility

Suppliers or experts that specialize in your industry may seem like the logical choice but it actually introduces some risk. However diversified injection molding suppliers and experts bring a balanced scope of expertise and stability that strengthens your project. 

2. Appropriate Certifications

Understandably there isn’t a one-size-fits-all-industries approach to custom injection molding. However, you should go for suppliers and experts with rare and sought-after certifications such as MedAccred Plastics accreditation as they offer additional expertise that benefits your specific injection molding project. 

3. Quality Control

Injection molding requires precision. To that end, custom injection molding experts should have regimented processes in place. It’s imperative that you partner with suppliers and experts who understand how quality control factors in – not only as a molder’s internal mechanism but also as it translates to maintaining quality standards. 

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Injection Molding Specialist (Image Source: Shutterstock)

Professional guidance from material suppliers and experts is important in navigating material specification and performance data. By leveraging their expertise manufacturers are able to interpret material specifications for complex and technical parts, and evaluation of performance data that is compliant with the industry.


Before starting your injection molding project, it’s essential to define the objectives of the project clearly. Understanding what you want to achieve with your product guides your material selection.

You have to put factors such as your product’s intended function, its environment, and the desired lifespan into consideration for optimal material selection. If your product frequently experiences extreme temperatures, select a material with a high thermal resistance. If your product needs to be lightweight yet durable, consider high-strength plastics. 

By defining your objectives upfront, it becomes easier to select a material that fulfills your current needs and anticipates future demands.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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