Injection Molding Material Selection Guide: How Materials Impact Part Performance

Resin selection is one of the most important design decisions when it comes to creating plastic injection molded parts. The material influences a part’s flexibility and strength as well as its surface appearance and dimensional stability. Manufacturability is also largely determined by the choice of material. Resins have different flow, cooling, and shrinkage properties, which governs tooling requirements and cycle times.  

At Thogus, our engineers have proven material expertise. Since 1950, we’ve been the trusted injection molding partner for the world’s most highly regulated industries. We work with customers to find the best thermoplastic resin for their application. Read our injection molding material selection guide to better understand commonly used resin options. Our goal is to help you determine which option aligns with the performance needs of your part.  

Give us a call today for more personalized recommendations, or to learn about our injection molding capabilities. 

Common Injection Molding Materials and Their Applications 

Understanding available resin options is the first step in choosing the right material for your component. Below, our injection molding material selection guide highlights the properties and typical applications of commonly used plastic injection molding materials.  

ABS 

Acrylonitrile butadiene styrene (ABS) is versatile, amorphous thermoplastic known for its impact strength and dimensional stability. It also machines easily and holds paint or plating well. The result? A smooth cosmetic finish perfect for applications like consumer electronics housings and automotive interior parts.  

Polypropylene (PP) 

With superior chemical resistance and fatigue endurance, Polypropylene (PP) is a lightweight semi-crystalline resin that is naturally flexible. It is a cost-effective choice for living hinges, like those used for consumer packaging and automotive components. PP is also well-suited for medical parts as it can withstand repeated bending without cracking.  

Polyethylene (PE) 

Polyethylene (PE) offers reliable moisture chemical resistance along with impact toughness across a wide temperature range. This makes it ideal for many industrial components. Manufacturers also frequently use this low coefficient resin for containers and caps.  

Nylon (PA) 

Durable and wear-resistant, Nylon (PA) is an engineered plastic renowned for its high tensile strength and fatigue resistance. These properties mean it can deliver reliable performance under continuous mechanical stress and elevated temperatures. Nylon also absorbs moisture, so Thogus engineers account for potential dimensional changes during the design stage. Typical applications for nylon include gears, bushings, and structural automotive parts. 

Polycarbonate (PC) 

From eyeglasses to headlights and even life-saving surgical equipment, polycarbonate (PC) is used in a variety of applications. Delivering outstanding strength, as well as impact and heat resistance, PC is often preferred over other transparent resins like acrylic. 

Acetal (POM) 

As a highly crystalline engineering plastic, Acetal (POM) has low friction, high stiffness, and dimensional stability that lasts. These properties, along with wear and fatigue resistance, make POM best for components that face repeated motion like gears and bearings. 

PEEK and Other High-Performance Engineering Plastics 

PEEK and other high-performance engineering offer thermal resistance, chemical resistance, and mechanical strength that goes well beyond standard resins. They won’t degrade even after continuous exposure to extreme temperatures and abrasive chemicals. That’s why they’re ideal for demanding industrial and medical applications. 

Material Properties’ Impact on Injection Molding Design & Part Performance 

Choosing a material should occur early in the design process since resin characteristics affect gate placement, wall thickness, and cooling channel layout. The resin’s shrink rate also determines how tooling dimensions must be adjusted to meet the specified tolerances while its flow behavior influences how easily it fills intricate geometries.  

The material selection does not stop impacting the part after production concludes. Tensile strength and modulus define how much load a part can withstand before deforming, and impact resistance shapes how it responds to sudden force. Thermal and chemical resistance rule a part’s ability to withstand extremely high or low temperatures as well as abrasive substances.   

Injection Molding Material Selection Guide: Key Factors to Consider 

Our injection molding material selection guide continues with the top considerations teams should evaluate to determine the ideal thermoplastic for their application. 

Functional Requirements 

A part’s performance requirements should be the top priority when comparing material options. Engineers must determine the mechanical loads the part will endure in addition to the tension, compression, and repeated impact it will face throughout its lifespan. Fatigue resistance is the most important resin quality for components that need to withstand cyclical stress. Stiffness and flexibility are also key properties that influence a part’s functionality. 

Environmental & Operating Conditions 

Components rarely operate in controlled environments. That’s why when it comes to material selection, it is critical to focus on what conditions the component will be exposed to. Moisture, for instance, can cause some thermoplastics to swell or lose mechanical strength over time. Chemical exposure and prolonged UV contact can degrade certain plastics, leading to discoloration and embrittlement. Assemblies intended or outdoor use or other harsh environments should therefore use material formulations designed to withstand these conditions. 

Manufacturability 

Manufacturability is oftentimes the deciding factor for material selection. A resin that flows seamlessly through thin walls and complex geometries keeps injection pressures reasonable and minimizes the risk of short shots. Shrinkage and warpage tendencies also differ with resin options. Resins susceptible to these issues need tighter process control and more conservative wall-thickness targets. Cycle times and mold temperature demands also shift depending on the chosen resin, and that shift can impact the efficiency of the entire production. 

Aesthetic Goals 

With certain applications, the appearance of a material is just as important as its mechanical properties. Some resins create a glossy, cosmetic-grade surface finish, while others offer a matte or textured finish. Color consistency and pigment compatibility differ by resin family. Requirements for transparency or translucency further narrow the material shortlist, since only certain amorphous resins deliver true optical clarity. 

Production Volume & Expenses 

High-performance engineering plastics often come with a premium price, making them more cost-effective for lower-volume orders and high-value parts. Commodity plastics typically reduce material costs and support faster cycle times, making them better suited for larger production runs. Tooling expenses also play a role, since abrasive or high-temperature resins may require hardened steel molds that increase upfront investment. 

Material Additives and Reinforcements  

Material additives and reinforcements can boost a resin’s base properties such as its environmental resistance, mechanical durability, and manufacturability. Common additives include: 

• Glass fiber reinforcement 
• Carbon fiber reinforcement 
• Mineral fillers 
• UV stabilizers 
• Flame retardants 
• Impact modifiers 
• Lubricants and processing aids 

Call Thogus for Guidance on Material Selection & Expert Injection Molding 

If this injection molding material selection guide has been helpful, reach out to our team at Thogus today for more engineering support. With our material expertise and advanced injection molding capabilities, we create components and assemblies that are customized to their applications.