Injection Molding Plastics refer to plastic materials that can be heated and melted under specific temperature and pressure conditions, injected into mold cavities through injection molding machines, and solidified into the desired shape after cooling. These plastics need to meet certain physical, chemical, and processing performance requirements to ensure smooth mold filling, stable molding, and high-quality products during the injection molding process.
In this article, we will list 16 common types of plastic materials for injection molding. It’s important to note that some of these materials have limitations or require special conditions during the injection molding process.
16 Common Types of Plastic Materials for Injection Molding
PE (Polyethylene)
PE is a thermoplastic polymer, divided into LDPE (Low-Density Polyethylene) and HDPE (High-Density Polyethylene) according to density. LDPE has extremely high flexibility and excellent transparency, elongation at break >500%; HDPE has high hardness and strength, tensile strength ≥30MPa. It has excellent chemical stability, resistant to acids, alkalis, and organic solvents, and almost does not react with any chemical substances. Heat resistance is average: LDPE heat resistance ≤80℃, HDPE ≤120℃. Excellent electrical insulation, surface resistivity up to 10¹⁸Ω·cm. Poor weather resistance, requires addition of UV stabilizer to extend service life.
Applications: LDPE is mainly used in food packaging film, agricultural film, plastic bags; HDPE is widely used in pipes (water supply and drainage, gas pipes), injection containers (turnover boxes, pallets), fibers and non-woven fabrics. In addition, HDPE is also used to manufacture large storage tanks, trash bins, etc.
Considerations: LDPE is suitable for injection molding, processing temperature 160-200℃, mold temperature 30-60℃, suitable for complex thin-walled structures; HDPE processing temperature 180-260℃, mold temperature 50-80℃. Processing temperature must be controlled to avoid overheating and decomposition. LDPE has excellent fluidity but is prone to melt fracture at high temperature; HDPE has high melt strength, suitable for structural parts. Both materials are not sensitive to humidity and do not require drying. For outdoor use, carbon black must be added for UV resistance, or surface coating for protection. Low temperature resistance needs to consider brittleness at low temperatures, and cold resistance can be improved by blending modification (such as adding metallocene polyethylene) if necessary.
PP (Polypropylene)
PP has a low density (0.9-0.91g/cm³), light weight, and is the lowest density type among general-purpose plastics. It has strong chemical corrosion resistance, resistant to most acids, alkalis, and organic solvents, but will degrade under high temperature and long-term contact with strong oxidants. Good high-temperature performance, melting point 160-170℃, long-term use temperature up to 130℃. Impact resistance depends on toughening modification; unmodified PP has poor low-temperature toughness and is brittle. Average weather resistance, easily aged under UV radiation, requires addition of UV stabilizer to extend service life. Easy to process, good fluidity, suitable for injection molded products with complex shapes.
Applications: Used in the automotive industry to manufacture bumpers, instrument panel frames, interior parts, and external decorative parts; in household appliances such as housings, containers, fans, casings, etc.; in daily necessities such as plastic basins, buckets, toys; in medical equipment for parts requiring high-temperature disinfection; in the textile industry to produce polypropylene fibers used in ropes, textiles, and filter materials.
Considerations: PP is suitable for injection molding, processing temperature 180-260℃, mold temperature 40-80℃. Raw materials need to be dried to moisture content <0.1% to avoid hydrolysis and molecular weight reduction at high temperature. Un-toughened PP has poor low-temperature performance and needs to be toughened by blending rubber or using toughening agents (such as EPDM, SEBS). UV-sensitive, must add carbon black or other UV stabilizers for outdoor use. Avoid long-term contact with strong oxidants and aromatic hydrocarbons to prevent performance degradation. Its easy-flowing characteristics are suitable for thin-walled and complex structural parts, and fast mold filling and appropriate holding pressure strategy is recommended.
PVC (Polyvinyl Chloride)
PVC is diversified and can be divided into rigid (unplasticized or lightly plasticized) and flexible (heavily plasticized) according to the plasticizer content. Rigid PVC has high mechanical strength, chemical resistance, good heat resistance (≤60℃), but poor flexibility; flexible PVC has good flexibility, but strength and heat resistance decrease. Strong chemical resistance, resistant to acid, alkali, and oil, but not resistant to organic solvents and some oxidants. Processing performance depends on additives, and the choice of stabilizers needs attention. Environmental friendliness is affected by the type of plasticizer (such as phthalates), and environmentally friendly additives need to be selected.
Applications: Rigid PVC: pipes (water supply, gas pipes), window profiles, flooring materials, outdoor fences; Flexible PVC: wire and cable sheaths, floor leather, medical tubing, toys; decorative materials (artificial leather, wallpaper); automotive interior and decorative parts.
Considerations: Rigid PVC is suitable for injection molding (requires proper mold cooling system), processing temperature 160-200℃, mold temperature 30-60℃. Stabilizers need to be added during processing to prevent decomposition, and environmentally friendly heat stabilizers (such as calcium-zinc compounds) are recommended. Flexible PVC has poor heat resistance and is not suitable for high-temperature applications; flexibility needs to be adjusted through plasticizers, but environmental friendliness is limited. Strong chemical resistance, but not resistant to gasoline, benzene solvents, and strong oxidants. UV-sensitive, UV stabilizers must be added for outdoor use. Environmental issues need to pay attention to the type of plasticizers, preferably lead-free, cadmium-free stabilizers, and plasticizers that meet food-grade standards. Hydrogen chloride gas will be generated during processing, so exhaust and waste gas treatment systems are required to ensure safe operating environment.
PS (Polystyrene)
PS has high transparency (light transmittance 88%), easy to process, good fluidity, good rigidity but significant brittleness. Low notch impact strength, poor heat resistance (≤80℃), easy to soften and deform at high temperature. Good chemical stability, resistant to acid, alkali, organic solvents, but low moisture absorption and no need for drying. Average weather resistance, UV sensitive, UV stabilizer needs to be added.
Applications: Disposable tableware, toys, stationery; optical lenses, display instruments; electronic product packaging; stationery and educational supplies; non-contact components of medical devices.
Considerations: PS is suitable for injection molding, processing temperature 180-240℃, mold temperature 40-80℃. Good fluidity, suitable for complex-shaped products, but prone to deformation at high temperature. Poor impact resistance, high impact modified (HIPS) can improve, but transparency and gloss decrease. UV sensitive, long-term exposure requires addition of UV stabilizers. Raw material drying requires no special treatment, but avoid moisture that causes performance degradation. Good chemical corrosion resistance, but not resistant to polar solvents (such as ethanol, acetone) and strong oxidants. Good dimensional stability, suitable for light-load structural and decorative parts.
ABS (Acrylonitrile Butadiene Styrene Copolymer)
ABS has excellent comprehensive performance, balancing strength, toughness, and fluidity. Tensile strength between 40-60MPa, notch impact strength ≥15kJ/m², making it both strong and impact resistant. Surface gloss up to 85 or above, easy to paint and electroplate. Strong chemical resistance, resistant to acid, alkali, and most organic solvents, but long-term contact with strong oxidants will cause degradation. Moderate heat resistance, long-term use temperature ≤80℃, above which it will soften and deform. Poor weather resistance, UV exposure causes material yellowing, UV stabilizer needs to be added to improve.
Applications: Widely used in automotive interior parts (such as dashboards, door panels), exterior parts (grilles, mirror housings), home appliance housings (refrigerator panels, washing machine shells), and electronic product housings. ABS is also widely used in the toy field due to its easy processing and compliance with safety standards. In addition, ABS material is commonly seen in office automation equipment (such as printer and copier housings).
Considerations: ABS can be directly injection molded, recommended processing temperature 180-250℃, mold temperature 40-80℃. Note that material will soften above 80℃, and heat resistance can be improved by blending (such as adding SAN or ASA). Raw material must be dried before processing (moisture content <0.1%) to avoid hydrolysis leading to decreased mechanical properties. For outdoor use, carbon black or other UV stabilizers must be added to prevent yellowing. When blending with other materials (such as PC, PVC), processing parameters need to be adjusted to prevent decomposition.
PA (Polyamide, Nylon)
PA has high strength (tensile strength ≥70MPa), high toughness (notched impact strength ≥5kJ/m²), excellent wear resistance and self-lubricating properties. It has high water absorption, with a balanced water absorption rate of 2-8%, significantly affected by humidity, and moisture absorption increases in high-temperature environments. Heat resistance depends on reinforced modification; after glass fiber reinforcement (GF30%), it can withstand temperatures up to 150℃. Dimensional stability is affected by moisture absorption and requires pre-drying treatment. It has strong chemical resistance, resistant to oil and alkali, but sensitive to strong acids and some solvents.
Applications: In the automotive industry, it is used to make engine peripheral parts, fuel pipes, and seals; in machinery, used for bearings, gears, and shaft components; in electronics and electrical appliances, used for connectors, switch housings, and electrical casings; in textile machinery, for chemical fiber filaments and special yarns; in daily necessities such as sports shoe soles and seat belts.
Considerations: PA is suitable for injection molding, processing temperature 220-300℃ (depending on the grade), mold temperature 40-90℃. Thorough drying is required before processing to a moisture content <0.2% to avoid hydrolysis during processing which may cause molecular chain breakage and affect mechanical properties. High-temperature processing (>300℃) is prone to decomposition and smoke generation, so processing temperature and residence time should be controlled. Poor low-temperature resistance, brittleness increases below -40℃, it is recommended to use toughened PA grades. Glass fiber reinforcement can improve heat resistance and rigidity but may sacrifice toughness. Avoid stress concentration in design, and perform annealing treatment if necessary. It has good chemical corrosion resistance, but the type of contact medium should be considered to avoid solvents that are sensitive to PA.
PC (Polycarbonate)
PC has excellent transparency and impact resistance, light transmittance ≥90%, and notched impact strength can reach 60-120kJ/m². Excellent heat resistance, maintains stable performance from -40℃ to 120℃, long-term heat resistance up to 140℃. High dimensional stability, linear expansion coefficient (CTE) only 60-80ppm/℃. Good chemical resistance, but stress cracking may occur when exposed to strong alkalis and aromatic hydrocarbon solvents. Moderate weather resistance, short-term outdoor use shows no obvious change, long-term use requires the addition of UV stabilizers.
Applications: Widely used in optical instruments, such as eyeglass lenses, camera lenses, microscope components; used in electronics and appliances for manufacturing displays, protective covers, phone casings; in the automotive industry for headlamp covers, dashboard transparent covers; medical equipment such as goggles and transparent protective shields.
Considerations: PC is suitable for injection molding, processing temperature 230-320℃, mold temperature recommended at 80-120℃ to reduce internal stress. Moisture content should be <0.02%, must be fully dried before processing, otherwise hydrolysis will cause material fogging. Decomposes easily at high temperatures (>250℃), avoid prolonged residence time. To improve heat resistance and impact resistance, fillers such as glass fiber (GF) or calcium carbonate can be added, but transparency will be affected. Pay attention to avoid stress concentration points in design, and perform annealing treatment if necessary.
PMMA (Polymethyl methacrylate, Acrylic)
PMMA has high transparency and excellent optical properties, light transmittance up to 92%, excellent weather resistance, remains transparent after more than 10 years of outdoor use. Surface hardness is high (Mohs hardness 5), good wear resistance, but still more brittle than glass. Strong chemical resistance, common acids, alkalis, and oils have little effect, but organic solvents (such as acetone, dichloromethane) will dissolve or swell the surface. Moderate heat resistance, heat distortion temperature about 100-120℃, glass transition temperature 105℃.
Applications: Widely used in advertising industry for lightboxes, exhibition display racks; optical field for making lenses, light guide plates, lighting covers; in construction for daylighting panels, partition materials; used in automotive for headlamp covers, interior parts; in medical devices for making optical instrument components.
Considerations: PMMA is suitable for injection molding, processing temperature 180-250℃, mold temperature 40-80℃. Cooling speed and temperature should be controlled to avoid internal stress, and annealing treatment is recommended to eliminate stress. Low moisture absorption, dry to moisture content <0.04% before processing, otherwise bubbles and surface defects may occur. High brittleness, avoid sharp stress concentrations in design. Poor solvent resistance, avoid contact with acetone, alcohol and other organic solvents, UV absorbers should be added for long-term outdoor use to delay aging.
PBT (Polybutylene Terephthalate)
PBT has good mechanical properties and dimensional stability, with tensile strength ≥50MPa and high flexural strength. Low water absorption (<0.1%), excellent electrical insulation performance, can be used as a printed circuit board material. Good chemical resistance, resistant to oil and alkali, but average acid resistance. High heat resistance, glass transition temperature (Tg) around 80℃, can withstand temperatures up to 120℃ after reinforcement. Easy to process, good fluidity, suitable for fast injection molding.
Application: Automotive electronic connectors, ignition system components; home appliance terminals, switch bases; electronic and electrical sockets, relays; fiber fabrics (such as fiber-reinforced composites).
Considerations: PBT is suitable for injection molding, processing temperature 220-260℃, mold temperature 40-80℃. Pay attention to drying, moisture content <0.03%, to prevent hydrolysis impact. Glass fiber reinforced grades can improve heat resistance and mechanical properties, but slightly reduce fluidity. Weather resistance is average, UV stabilizer needs to be added for outdoor use. Good arc resistance, suitable for electronic and electrical fields. Temperature control is needed during processing to avoid decomposition gas. Mold cooling should be fast to reduce warping.
PET (Polyethylene Terephthalate)
PET has excellent transparency (light transmittance ≥85%), mechanical strength (tensile strength ≥50MPa), and chemical corrosion resistance. High crystallinity requires pre-drying before processing, mechanical properties decrease after moisture absorption. Good heat resistance, can withstand high temperature for short term, long-term heat resistance up to 120-130℃. Good electrical insulation, can be used as electronic component materials. High dimensional stability, suitable for precision injection molding.
Application: Beverage bottles, food packaging; fiber fabrics (polyester, PET fabrics); optical lenses, display panels; electronic and electrical housings; reinforced base material for engineering plastics.
Considerations: PET is suitable for injection molding, drying recommended (moisture content <50ppm), processing temperature 260-290℃, mold temperature 30-70℃. Glass fiber reinforced grades can improve heat resistance and mechanical strength, but transparency will decrease. Avoid contact with strong acids, strong alkalis, and organic solvents during long-term use. High dimensional stability, suitable for high-precision products. Weathering agents are recommended for outdoor use to extend service life.
HIPS (High Impact Polystyrene)
HIPS is an engineering plastic modified by adding rubber tougheners into PS matrix, impact strength is 5-10 times higher than ordinary PS. Good coloring and processability, smooth surface with high gloss. Average chemical resistance, weak acid and alkali resistance, not suitable for strong corrosive environments. Low heat resistance, long-term use temperature ≤80℃, easy to soften at high temperature. Dimensional stability is acceptable, but shrinkage at high temperature is large, mold design needs attention. Excellent impact resistance, but slightly inferior transparency and glossiness compared to PS.
Application: Home appliance housings (such as TV casings, washing machine housings), toys, stationery, daily necessities, automotive interior parts (such as door panels, dashboard components).
Considerations: HIPS is suitable for injection molding, processing temperature 180-240℃, mold temperature 40-80℃. Need to choose high-quality tougheners to prevent performance degradation due to aging. Easy to soften at high temperature, avoid long-term high-temperature processing, or choose heat-resistant modified HIPS grades. Dimensional stability is affected by temperature, mold cooling system and holding pressure parameters need adjustment. Weather resistance is average, UV stabilizers recommended for outdoor use. Raw material drying to moisture content <0.1% to avoid silver streaks and bubbles caused by moisture. Avoid stress concentration design, as tougheners may reduce stress cracking resistance.
PPS (Polyphenylene Sulfide)
PPS has excellent heat resistance (continuous use temperature 200-240℃), excellent chemical resistance (almost resistant to all reagents). Balanced mechanical properties, high rigidity and good toughness. Very high dimensional stability, very low thermal expansion coefficient. Excellent electrical insulation, can be used as material for high-frequency electronic components. Good self-lubricating, low coefficient of friction.
Application: Automotive industry (exhaust treatment system, sensors); electronics and electrical (high temperature connectors, substrates); chemical equipment (corrosion-resistant pipelines, pump parts); aerospace (high temperature components).
Considerations: PPS is suitable for injection molding, processing temperature 280-340℃, mold temperature 120-160℃. Pre-drying to low moisture content is recommended to prevent hydrolysis. Excellent heat and corrosion resistance, suitable for extreme conditions. High processing difficulty, requires high-performance injection machines and molds. Mold design needs optimized venting system to prevent gas retention. UV stabilizers needed for outdoor use, but high cost should be comprehensively considered.
PTFE (Polytetrafluoroethylene, Teflon)
PTFE is known as the “King of Plastics”, with extremely good chemical stability, almost no reaction with any chemical substances. Excellent high and low temperature resistance (-196℃ to 260℃), high dimensional stability, low thermal expansion coefficient. Outstanding electrical insulation, very low dielectric constant and dielectric loss, suitable for high-frequency applications. Good self-lubrication, very low friction coefficient (as low as 0.04), excellent anti-adhesion. Relatively soft mechanical properties, low tensile strength, poor wear resistance, easy to creep during long-term use. High processing difficulty, requires high-temperature sintering process.
Application: Chemical industry (corrosion-resistant pipelines, valves, linings); electronics and electrical (high-frequency insulation materials, cable insulation); aerospace (seals, high-temperature insulation materials); food industry (non-stick coatings, food processing equipment linings); medical field (artificial blood vessels, seals).
Considerations: PTFE requires sintering process, conventional injection molding is not suitable, but since users may need to understand plastic material characteristics, briefly: high processing difficulty, requires high temperature (350-400℃) and specialized equipment. Strong chemical resistance, suitable for corrosive environments, but very high processing cost. Excellent heat resistance, but poor low-temperature toughness, needs to be improved by filler modification. Excellent anti-adhesion, need to avoid sticking to mold during processing. High cost, recommended for extreme condition applications only. Excellent weather resistance, no special protection needed for outdoor use. Fluorine-containing gases generated during processing must be strictly controlled to meet environmental requirements.
UPE (Ultra-high Molecular Weight Polyethylene, UHMWPE)
UPE has ultra-high molecular weight (usually >1.5 million g/mol), making its wear resistance the best in the world (friction coefficient <0.1), excellent self-lubrication, strong impact resistance (notched impact strength ≥100kJ/m²). Strong chemical resistance, resistant to acid, alkali, and organic solvents, good electrical insulation. Low density but not high strength (tensile strength ≈30-40MPa), poor heat resistance (≤100℃), low glass transition temperature. Excellent low-temperature toughness, can maintain performance at -269℃. But low thermal deformation temperature, not suitable for high-temperature environments.
Application: Conveying machinery (sliders, guides, wear-resistant linings); textile industry (conveyor belt parts, spinning components); medical artificial joints, dental parts; food processing machinery (wear-resistant parts, seals); corrosion-resistant linings in chemical industry; marine engineering and ship parts.
Considerations: UPE is difficult to inject (requires special equipment and process), processing temperature 200-240℃, mold temperature must be strictly controlled. Due to high molecular weight, melt viscosity is extremely high, requires high torque injection machine and special screw design. Strong chemical resistance, but not suitable for high-temperature environments, softens easily above 100℃ for long-term use. Good impact resistance, but performance decreases in high temperature. Mold design needs attention to prevent trapped gas during processing. Wear resistance is its biggest advantage, model selection should be based on load. High cost, recommended for extremely wear-resistant environments. Good weather resistance, UV impact in outdoor use needs attention, anti-aging performance can be improved by additives.
PEEK (Polyether ether ketone)
PEEK is a high-performance thermoplastic engineering plastic with excellent heat resistance, with continuous use temperature up to 250℃, and can be used for a short time at even higher temperatures. It has strong chemical corrosion resistance, almost resistant to all chemical media, including strong acids, strong alkalis, and organic solvents. It has excellent mechanical properties, tensile strength ≥90MPa, balancing rigidity and toughness, with excellent creep resistance and fatigue performance. Good electrical insulation performance, stable dielectric constant, dielectric strength up to 25kV/mm. Good dimensional stability, low coefficient of thermal expansion (CTE＜5ppm/℃), suitable for precision part manufacturing. Good self-lubrication, low friction coefficient, widely used in wear-resistant parts.
Applications: In aerospace field, used to manufacture high-temperature-resistant engine parts, insulation materials; in medical devices, used to make artificial joints, dental implants and surgical instruments; in electronics and electrical industry to make high-temperature connectors, high-temperature resistant substrates and electrical insulation components; in chemical industry for seals and corrosion-resistant pipelines; in automotive industry for high-temperature resistant parts and structural reinforcements.
Considerations: PEEK is suitable for injection molding, but processing is relatively difficult. It is recommended to use a processing temperature of 350-400℃, and mold temperature needs to reach 150-200℃ to ensure good molding and dimensional stability. Raw materials need to be of high purity, pre-dried to moisture content <0.02% to prevent hydrolysis during processing. Equipment requirements are high, need high torque and high temperature resistant materials (such as PEEK-special injection molding machine, high temperature mold steel). Mold design needs to optimize gating system and venting system to prevent weld lines and bubble defects. Processing cycle is long, need to control holding pressure time and cooling rate. Material cost is high, recommended to be used in scenarios with high performance requirements.
POM (Polyoxymethylene, also called Acetal or Delrin)
POM has excellent rigidity and hardness, tensile strength ≥60MPa, outstanding wear resistance, low friction coefficient (only 0.15), excellent self-lubricating properties. Extremely high dimensional stability, water absorption rate <0.2%, little affected by humidity, able to maintain long-term stable fitting accuracy. Strong chemical corrosion resistance, resistant to acid, alkali and most organic solvents, but not resistant to strong acids like concentrated sulfuric acid and concentrated nitric acid. Heat resistance is average, long-term use temperature ≤120℃, easy to decompose at high temperatures.
Applications: In automotive industry used to manufacture precision gears, bearings, sliding components; in machinery industry to make automation equipment parts, guide rails; in electronics and electrical as connectors, switch housings; also widely used in precision instruments and household appliances.
Considerations: POM is suitable for injection molding, processing temperature 160-210℃, mold temperature 60-100℃. Must be fully dried before processing to moisture content <0.2%, otherwise formaldehyde gas will be generated under high temperature, affecting product performance. Avoid high-temperature long-time processing to prevent material degradation. Brittleness increases under low temperature (<-40℃), need to use glass fiber reinforcement to improve low-temperature resistance. Mold design should pay attention to the venting system to prevent gas from causing pores or surface defects. If there are special requirements for lubrication, silicone oil or other additives can be selected.
Finally, if you are considering which material is suitable for your project? Generally speaking, when we understand the characteristics of these plastics, we can make a good choice. But if you are still not sure, you can try small batch prototyping first, then verify molding effect and observe the performance of the product in the usage environment. The benefit of doing so is that it can avoid rework or scrapping after mass production.
Also, don’t forget to consult the company providing injection molding service for you, such as rjcmold, a factory with more than 20 years of injection molding service experience, can provide free technical support.
