Types of Plastic Materials Used in Injection Molding


Choosing the right material is the critical first step in plastic injection molding. The type of thermoplastic resin used plays an essential role in the mold’s design, the part’s wall thickness, strength, durability, molding temperature, molding parameters, cycle times, and how the finished plastic part holds up under different operating conditions, environments, and temperatures.

In this article, we’ll cover some of the most common injection molding materials, explain their differences, and provide guidance on selecting the best one for your application.

Polypropylene (PP)

PP is a lightweight, low-cost plastic with great mechanical properties, including strong tensile strength and good chemical, impact, and fatigue resistance. It’s also known for its moldability, and its ability to endure hot and cold environments without a significant loss in physical properties.

PP is commonly associated with food packaging, as it is a good material for microwaveable containers. It also has multiple industrial and structural applications for equipment and machinery.

For example, the automotive industry uses PP for instrument panels, bumper trim, car battery trays, dashboard components, and other interior and exterior parts. It is also in high demand within the medical industry.

Polyethylene (PE)

PE is similar to PP, and it’s still a durable, low-cost, lightweight plastic with moldability, and good impact, chemical, and corrosion resistance. It also has strong weatherproofing characteristics and good toughness at very low temperatures.

PE is often used to produce houseware items like containers. It is also ideal for industrial applications where moisture resistance is essential. The automotive industry uses the material for numerous interior and exterior components like fenders, panels, fuel tanks, and electrical insulation. The medical industry uses the material for its implants and prosthetics.

Acrylonitrile Butadiene Styrene (ABS)

ABS is another low-cost, durable thermoplastic with excellent stiffness, good tensile strength, high machinability, abrasion resistance, and impact resistance.

Multiple industries rely on ABS as an electrical insulator. It is an ideal material for computer dashboards, user-interface control panels on equipment and machinery, printers, and electrical enclosures.

ABS is also heavily used for industrial pipes and fitting within the commercial and industrial construction markets. When using an FDA-compliant grade, ABS is used for food storage and packaging Household gardening tools, vacuum cleaners, and other consumer appliances are made from ABS material.

In the automotive industry, ABS is used to make dashboard components, instrument panel parts, seat trims, and wheel covers.

Polycarbonate (PC)

Once an essential material within the optical media industry, polycarbonate (PC) is an extremely durable material with superior tensile strength, good bend/flexural strength, and excellent weather, heat, impact, abrasion, flame, chemical, and UV resistance.

Its excellent optical qualities make it an ideal replacement for glass. In fact, it’s up to 250 times stronger than glass. The material’s ability to withstand direct impacts and strong weathering resistance is largely why the automotive industry uses polycarbonate for headlight lenses, and interior light lenses and enclosures.

PC is also a good electrical insulator, which makes it a nice material in multiple electronic applications. Other industries combine its superior strength and optical qualities to make, durable, and often impenetrable windows, lenses, street lamps, and light enclosures.

Thermoplastic Polyurethane (TPU)

TPU has the highest tensile strength and unmatched bend/flexural strength of all the materials on this list. Known as an extremely tough and durable material, TPU is known for being flexible yet very tough with excellent impact, abrasion, solvent, grease, and oil resistance.

Automotive and industrial manufacturers use TPU for timing and transmission belts, multiple pressure gaskets, seals, bushings, and interior car parts like cup holders, and glove boxes. The material is also used in conveyor belts in multiple manufacturing environments and for medical devices, hoses, and power tools.

Comparing Different Injection Molding Materials

Choosing the right injection molding material comes down to your specific application. Selecting the best plastic polymer for your injection molding project will involve making sure it will accommodate your finished part’s wall thickness, operating temperatures, visual requirements, and operating conditions. In addition, your injection molding supplier will help prevent specifying a plastic material that is too expensive for the target per-unit cost of your part.

While there are thousands of different plastic materials and grades, the unique attributes you need for your part should always be discussed with your chosen plastic injection mold manufacturing supplier. They will have experience with these materials and provide critical guidance on costs, cycle times, wall thickness, and other vital parameters.

What Other Factors Should be Considered When Choosing a Plastic Material?

Besides choosing a plastic material with the proper physical and functional performance properties for your injection molded parts, the cost and availability of the material are very important. As mentioned above, there are thousands of plastic types and grades to choose from. Many of them are manufactured outside the USA in Europe or Asia. European-made materials tend to be high-performance engineering-grade plastics that cost a lot and have long lead times and large minimum order sizes. Plastic materials made in the USA and Asia tend to be lower-cost commodity types that are more commonly stocked with shorter lead times

Again, your injection molding supplier should be able to help guide you toward materials that will be a good match for your injection molded parts.  .

What Materials Are Used the Most and Why?

Of all the materials available to manufacture custom molded parts, commodity polymers like polyethylene, polypropylene, and ABS grades are the most commonly used materials for injection molding by usage.

Polypropylene and polyethylene are typically the most affordable thermoplastics. However, it’s important to note that the pricing of these materials is volatile since they are a derivative of natural gas and crude oil. Affordability should not be the main factor in choosing a material—your main priority should be selecting an injection molding material best suited for your specific application.

Get Design Assistance From MSI Mold

Founded In 2005, MSI Mold is a reliable U.S.A. plastic injection molding manufacturer offering a wide range of in-house services and capabilities, including mold design, prototyping, and assembly.  Our experienced mold makers and engineers are dedicated to helping customers through the entire process, from material section and mold design to production. Please visit our blog for more plastic injection molding resources. If you need help selecting the best injection molding material for your product, please contact us today to schedule a free design consultation.