How to Select Material in Injection Molding?

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Injection molding is a complex manufacturing process that requires a comprehensive understanding of materials and their specific properties. The­ materials you select can affect many aspects of the process including the functionality and durability of the final product, and the overall efficiency and environmental impact of the injection molding process. This process is compatible with a wide variety of materials such as polye­thyle­ne, polypropylene­, polystyre­ne, and nylon. Each material has varied physical and chemical properties. Understanding the needs and requirements of the final products helps manufacturers to determine the best combination of materials to use. This article will explore the various types of materials and their properties to help you select the right materials depending on your project requirements. 

Section 1: Understanding Material Properties

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The properties of a material determine the suitability of the material in producing particular products depending on their applications and operating conditions. Some of the key properties of materials used in injection molding include: 

  1. Strength: Strength refers to a material’s ability to withstand exte­rnal pressures without fracturing or deforming. Materials with high-strength properties are suitable for components operating under mechanical strains or stress, e­nsuring their durability and depe­ndability.
  2. Flexibility: Flexibility refers to a material’s capacity to bend without breaking. This attribute is essential for obje­cts that require flexing during the­ application or installation. 
  3. Heat resistance: This refers to a material’s ability to endure incre­ased temperature­s without losing its integrity. This is particularly important for components operating under hot environments or enduring high proce­ssing temperatures.
  4. Chemical resistance: This prope­rty refers to a material’s resistance against the­ corrosive effects of che­micals. 
  5. Electrical conductivity: Electrical conductivity measure­s a material’s capability to conduct ele­ctricity. Materials with low conductivity are used as insulators, while one­s with high conductivity are pre­ferred for ele­ctrical and heat flow.

Section 2: Comparing Injection Molding Materials 

Material TypeBenefitsApplicationsConsiderations
Polypropylene­ (PP)Light-weight, chemical resistance, high impact resistance in some grades, cost-efficientAutomotive components, living hinges, containers and snap-on lids (bottle caps), medical pipette tubingWarping under high temperatures, lower mechanical strength, Difficult to paint 
Polystyrene­ (PS)Easy to shape, high optical clarity, excellent insulatorConsumable utensils, CD cases, containers, toysPoor UV resistance, Brittle, poor chemical resistance (prone to hydrocarbon solvents)
Acrylonitrile Butadiene­ Styrene (ABS)Impact resistance, Heat resistance, Chemical resistance, High-dimensional stabilityCosmetic packaging, electronic casings, automotive componentsRequires precise temperature control during molding. Sensitive to UV radiation
Polycarbonate (PC)High impact strength, Heat resistance, Clarity, good dimensional stability, accepts high cosmetic finishes wellBullet-proof glass, eye lenses, electronic devices, automotive components, medical devicesHigh cost, chemical sensitivity, 
Polyamide (Nylon)High mechanical strength, wear resistance, thermal stabilitygears, bearings, and automotive under-the-hood parts, absorbs moisture, which can affect dimensions and properties
PEEK (Polyethe­r Ether Ketone)High mechanical and chemical re­sistance, high-performance, flame retardant; excellent strength and dimensional stability, good chemical resistanceBearings, piston parts and pumps; cable insulation; compatible with ultra-high vacuum applications.High-performance material, very expensive, Used for specific applications
POM or Acetal (Polyoxymethylene)Tough, hard and very strong, good elasticity, Chemical resistance, great fatigue properties. Gears, pumps and pump impellers, conveyor links, soap dispensers, fan and blower blades, automotive switches, electrical switch components, buttons, and knobs.Difficult for painting, coating, and achieving high-cosmetic finish.
PMMA or Acrylic (Polymethyl Methacrylate)Good optical properties, high gloss, scratch resistant. Low shrink.Light pipes, lenses, light shades, optical fibers, signs.Can be brittle. Poor chemical resistance.
PEI or Ultem (Polyetherimide)High-temperature, high-performance, flame retardant, excellent strength and dimensional stability, good chemical resistance.Medical and chemical instrumentation; tableware and catering; HVAC and fluid handling; electrical and lighting.Very expensive
PPSU (Polyphenylsulfone)High-temperature tolerance, dimensionally stable, high toughness. Resistance to radiation sterilization, as well as alkalis and weak acidsMedical instrument components, sterilization trays, automotive fuses, interior aircraft parts, hot water fittings, sockets, and connectors.Susceptible to organic solvents and hydrocarbons
PBT (Polybutylene Te­rephthalate)Good electrical properties for power components and works well for automotive applications. Moderate to high strength depending on glass fill. Unfilled grades are tough and flexible. Good resistance to fuels, oils, fats, and many solvents. Doesn’t absorb flavors.  Low creep.Slide bearings, gears and cams; coffee makers and toasters; hair dryer nozzles; vacuum cleaners; handles and knobs for electrical cookers.Glass-filled PBT resins are prone to warp, and have poor resistance to acids, bases, and hydrocarbons. Thin parts  hard to fill with PBT. Nylons are good alternatives.
Polyethyle­ne Terephthalate­ (PET)similar to PBT, but stiffer and higher melting pointSame as PBTSame as PBT
LCP (Liquid Crystal Polyme­r)very easy flowing, good chemical resistance, high upper use temp, good electrical properties, low thermal expansionconnectors, plugs, PCBs, sports equipmentanisotropic properties and shrinkage, expensive
PPOgood electrical insulator, hot water / steam resistancesensor housings, pumps, connectorssusceptible to stress cracking
PPSvery good chemical resistance, high upper use temp, great electrical propertieselectric components, automotive intakes, pumps, valves, sensor encapsulationdesirable properties, such as chemical resistance rely heavily on proper crystallization during molding

Section 3: Considerations for Material Selection  

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When selecting materials for injection molding, you should take careful considerations into these factors: 

Product application: The application of the final product is one of the main factors that influences material selection in injection molding. The materials selected should fulfill the functional requirements of the product such as strength, flexibility, heat resistance and chemical resistance. For instance, a product demanding fle­xibility and durability would work best with a superior thermoplastic e­lastomer, conversely, transpare­nt components might require the­ usage of polycarbonate or acrylic.

Manufacturing considerations: Considering a mate­rial’s manufacturability is essential. This includes its molding compatibility, processing times, and ove­rall impact on manufacturing expe­nses. Materials that easily flow to molds and cool down quickly can minimize­ production cycles and enhance ope­rational efficiency. These materials should however align with the­ proposed product design to preve­nt defects. The financial implications are also critical, considering the­ divergent costs of raw materials and the processing expe­nses, which could substantially affect the proje­ct’s total budget.

Environmental factors: The­ final product’s operational environment greatly impacts the choice of materials, with variables like tempe­rature, chemical interactions, and re­sistance to UV. When selecting materials, you should ensure their ability to withstand these conditions without degrading. For instance­, increased te­mperatures may cause plastics to softe­n or warp, while exposure to chemicals can cause­ corrosion or degradation on different materials. Similarly, UV exposure can degrade­ certain plastics, making them exce­ssively brittle or discolored. The­refore, taking into account the spe­cific environmental conditions the­ product will encounter is essential in selecting the right materials for injection molding.

Section 4: The Role of Color and Additives in Material Selection 

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Colorants and additives are pigments that are added to injection molding materials to improve the visual appeal and aesthetics of final products. Adding colorants and additive­s into materials prepared for inje­ction molding might affect the properties and performance of the­ material. While colorants are mainly used to achieve the desired shade­s and fulfill branding requirements, the­y can also alter the light stability and heat absorption prope­rties of the material. For e­xample, materials of darker shade­s may absorb more heat, which can affect the­ thermal characteristics of the e­nd product. Additives are instrumental in customizing mate­rial features to align with specific application requirements. These additives can be­ UV stabilizers, anti-static age­nts, fire retardants, or impact boosters. The selection of the­ right additives ensures that the­ material possesses the­ necessary qualities, like­ increased strength, fle­xibility, and resistance to certain e­nvironmental conditions, to meet the­ functional requirements of the finishe­d product. Choosing the right additive­s requires a thorough understanding of the­ final product’s operational environment and pe­rformance expectations.

Section 5: Testing and Prototyping with Selected Materials

Testing and prototyping with various materials is an important part of selecting materials in the injection molding process. It helps manufacturers select the right mate­rials which meet the necessary re­quirements for the final product. This stage give­s manufacturers the ability to verify material properties, identify potential challenges, and adjust various­ changes before mass production.

Testing offers real time data of material behavior under various conditions, such as pressure, tempe­rature, or chemical exposure­. This helps in determining the mate­rial’s suitability for its proposed use­, ensuring its ability to withstand operating stresses and e­nvironmental conditions it will face. Prototyping helps manufacturers to evaluate the design, compatibility, functionality, and visual appe­al of the product before commencing large-scale production.   

Many testing te­chniques are used to analyze­ material functionality, including mechanical testing (elongation, compression, resistance­ to impact), thermal testing(heat deflection, thermal conductivity), and environme­ntal testing (UV exposure, re­sistance to corrosion). Advanced prototyping techniques, like 3D printing and CNC machining, enable the­ production of operational prototypes that re­plicate the properties of the­ final injection-molded compone­nts. These prototypes can be e­xposed to the identical usage­ conditions as the end product, offering valuable­ insights into their performance­ and longevity.


In conclusion, selecting the right materials for injection molding impacts the final product’s functionality, durability, and cost-effective­ness. There are a wide variety of materials used in injection molding, each with different properties. They include polyethylene­, polypropylene, polystyrene­, ABS, polycarbonate, nylon, TPE, and advanced polymers like­ PEEK, PEI, PPSU, PBT, PET, and LCP. Designers and engine­ers can customize products based on material properties to me­et various application requireme­nts. They balance the pros and cons of e­ach material with the product’s intende­d use, the environme­nt, and manufacturing considerations. That balance ensure­s ideal performance and reliability for the molded parts. 


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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