Injection molding has become so widely used because it is extremely versatile and flexible. The process allows us to mold components from many different materials into virtually any shape. However, there are several plastic resin types on the market today. Choosing the right materials will directly affect the success or failure of the product. Otherwise, you will run into serious problems like warping or shrinkage, even cracking. I will show you the 10 materials that are best suited for injection molding services.
ABS (Acrylonitrile Butadiene Styrene)
ABS is a very popular thermoplastic injection molding material in manufacturing today.This material has a good balance of strength, toughness and ease of processing, and can maintain good physical impact resistance in low temperature environments.
Through ABS machining, it can be made into a series of plastic parts such as automotive interior parts and electronic product casings. The cost performance is very high. This type of product is also more suitable for indoor use or projects with high requirements for appearance treatment. The cost performance is very high. And products made of ABS are also more suitable for indoor use or projects with high requirements for appearance treatment.
Engineer’s Tip:
ABS material is primarily used for cosmetic parts. Sink marks and weld lines can occur on cosmetic surfaces. When designing your parts, you should follow the 60% rule to avoid surface depressions. This rule states that the thickness of any internal ribs or bosses shall not exceed 60% of the thickness of the adjacent main wall. In addition, gate placement and optimized injection speed are also key practices for you to control weld lines on non-cosmetic surfaces.
PP (Polypropylene)
PP is a fairly durable thermoplastic polymer and an excellent high-frequency insulating material. It has excellent fatigue resistance and excellent chemical resistance. In addition, the density of polypropylene is usually between 0.89 ~ 0.92 g/cm3.
Therefore, polypropylene is well suited for car bumpers and interior parts, medical syringes, and food containers. If you choose polypropylene injection molding to make your own products, the price advantage is also obvious.
Engineer’s Tip:
The most outstanding characteristic of polypropylene is its resistance to flexural fatigue. This also makes the material a preferred choice for hinge design. However,the success of a hinge relies on mold design and gate placement. The gate must be positioned to force the molten polymer to flow perpendicular to the hinge axis.
In addition, PP has a high shrinkage rate (1.5%−2.5%), and uniform wall thickness and a highly optimized cooling system are absolutely necessary to prevent serious warping problems.
PE (Polyethylene)
In injection molding, PE (Polyethylene) is the plastic with the largest global production and widest application. high-density polyethylene (HDPE), which has high rigidity, high tensile strength, and opaque; Low-density polyethylene (LDPE), which is highly ductile and translucent.
Polyethylene has excellent moisture and chemical resistance, and is extremely resistant to most acids, alkalis and solvents. And the material can still remain non-brittle even if it is used in an environment of tens of degrees below zero. At the same time, this material is non-toxic and odorless, and complies with FDA and medical standards.
Injection molded parts made of polyethylene include industrial containers, pipe joints, flexible bottle caps, medical ear cleaning balls, food preservation boxes, etc.
Engineer’s Tip:
PE (especially HDPE) is a highly crystalline material. This means it will shrink dramatically when cooling and solidifying. Uneven wall thickness in your polyethylene part will cause extreme warping problems. Additionally, PE has an extremely low surface energy, so you cannot simply glue or paint PE parts, and the adhesive will simply peel off.
PC (Polycarbonate)
PC is a tough, engineering-grade thermoplastic. The material offers extremely high impact resistance and excellent optical clarity. Even in high-temperature environments, Polycarbonate can maintain good physical properties. Therefore, if your components need to be used in harsh environments, then PC material is definitely one of the good choices.
You can use polycarbonate injection molding to produce a wide variety of components, such as medical devices and protective face shields, electronic display panels, automotive headlight covers, and more.
Engineer’s Tip:
PC is a hard, high-viscosity resin. It is extremely difficult to flow through thin walls. This means you need larger gates and runners, as well as extremely high injection pressure.
And there’s another problem you might easily overlook: the internal stress of PC material. If your mold is too cold, the material will freeze too quickly, thus locking huge internal stresses inside the parts. It could lead to failures of your components. I suggest using high mold temperatures(mostly 80℃-120℃).
POM (Acetal)
POM, also commonly known as acetal. This material possesses high rigidity and hardness, and is an engineering plastic with extremely high yield strength. Moreover, POM is a naturally self-lubricating material. Its surface has an extremely low friction coefficient, so the surface is very smooth.
In terms of appearance, POM plastic is naturally opaque and white. In terms of performance, POM materials have excellent dimensional stability. It has extremely low water absorption, so POM components maintain their precise dimensions even in humid environments. Additionally, the material can withstand long-term loads without deformation.
Because of these excellent properties, POM materials have become an ideal material to replace metals in manufacturing. Nowadays, injection-molded POM components include transmission gears and shafts, bearings, pulleys, car door lock components, high-performance fasteners, etc.
Engineer’s Tip:
POM has extremely poor thermal stability. If the melt temperature is too high, POM will quickly degrade into formaldehyde gas. This gas is toxic. And you must never mix POM and PVC without thoroughly cleaning the barrel. This is because their chemical reaction is explosive.
In order to ensure the dimensional accuracy of thick-walled gears, you also need to control the holding pressure extremely professionally to compensate for the extremely high shrinkage of POM materials (about 2.0%).
Nylon (PA– Polyamide）
As one of the most widely used injection molding materials, nylon is popular for its excellent performance. This material has excellent self-lubricating properties, a low coefficient of friction, and outstanding tensile and impact resistance.
At the same time, precisely because nylon has strong resistance to engine oil, grease, and various solvents, it is also widely used in mechanical transmission parts (gears, bearings, cams), automotive engine compartment peripheral parts, industrial cable ties and fasteners, and power tool housings.
Engineer’s Tip:
Nylon is highly hygroscopic. It not only absorbs moisture from the air before injection molding but also absorbs water throughout its usage. If you do not dry the resin thoroughly before injection molding, the moisture inside it will turn into steam, making the part extremely brittle. Also, keep in mind that injection-molded nylon parts can exhibit dimensional changes of up to 2% when they absorb water in real-world environments. Therefore, please be sure to reserve this tolerance during assembly design.
Acrylic (PMMA)
Those of you who are familiar with CNC acrylic services must know the advantages of acrylic. It has a light transmittance of 92%, which is better than most glass, and it also has ultraviolet (UV) resistance and will not turn yellow when used outdoors for a long time. Therefore, acrylic is often used as a substitute for glass.
In addition, this material is scratch-resistant and can be dyed into various bright and transparent colors. Thus, in the manufacturing industry, acrylic is often used to make car taillights and instrument panel covers, optical lenses, billboards, packaging boxes, and other components.
Engineer’s Tip:
Acrylic is incredibly notch-sensitive. When designing, you must pay close attention to sharp corners of components. This is because sharp corners become stress concentration points, and parts are almost certain to crack even under very small loads. So be sure to use generous fillets (larger R-values) on all interior corners.
One more thing to note is that during the injection molding process, if the mold temperature is too low, PMMA is prone to generating internal stresses. This stress may not be immediately apparent, but may also lead to the development of microcracks when the part is later exposed to chemicals or UV light.
PEEK (Polyether Ether Ketone)
PEEK can be said to be the performance ceiling in the plastics industry. This material possesses extreme high-temperature resistance, capable of being used at temperatures up to 250 degrees Celsius. It can also maintain extremely high tensile and bending strength at high temperatures.
At the same time, PEEK materials also have excellent biocompatibility. This means it can also be used for medical implants, such as artificial spines, dental accessories and more. As for other peek components, there are aerospace structural parts, semiconductor processing equipment parts and internal wear-resistant parts of automobile engines.
Engineer’s Tip:
PEEK materials require extremely high processing temperatures. Its melting temperature is usually above 380°C, and the mold must be heated to 160°C–200°C. Standard mold steels will rapidly degrade under these conditions, and you must use high-quality heat-treated steels (such as H13) to manufacture molds.
PET (Polyethylene Terephthalate)
PET is also a thermoplastic polymer and a widely used polyester material in the injection molding industry. This material has high strength and rigidity, and can maintain its physical properties over a wide temperature range.
Additionally, PET material has excellent barrier properties and supports environmental recyclability. Major PET injection molded products include medical blood collection tubes and consumables, electronic connectors and switch components, as well as purified water bottles.
Engineer’s Tip:
The core of injection molding PET lies in controlling the crystallinity through mold temperature. If you need transparent injection molded parts, then you need a cold mold to allow the material to freeze quickly into an amorphous state. However, if you need injection-molded parts with high heat resistance and high strength, you must use a hot mold to crystallize the PET, which will make it opaque.
PVC (Polyvinyl Chloride)
PVC is a very low-cost plastic material. Because the material contains chlorine, it will automatically extinguish after leaving the ignition source, so PVC has excellent flame retardancy. This material also has excellent chemical resistance and is extremely resistant to acids, alkalis, and salts.
As for hardness, you can change from an extremely hard material (UPVC) to an extremely soft material (soft PVC) by adding plasticizers. In the injection molding industry, you can make PVC materials into construction pipes and fittings, infusion pipes, wire and cable insulation sheaths, door and window profiles, etc.
Engineer’s Tip:
PVC has extremely poor thermal stability. If the melt temperature is too high, or even if it remains in the barrel one extra minute too long, it will degrade and emit extremely corrosive hydrochloric acid (HCl) gas, which will make standard steel molds rust and pit the machine’s screw.
For these reasons, when injection molding PVC you absolutely must use corrosion resistant stainless steel molds, Therefore, when injection molding PVC, you must use corrosion-resistant stainless steel molds (such as 420SS) and also ensure perfect temperature control. You cannot allow the material to continue baking in the barrel when the machine is stopped.
Top 10 Common Plastics Overview
| Material | Core Performance | Cost | Manufacturability | Typical Injection Molded Parts |
| ABS | Excellent overall mechanics, good impact resistance, highly receptive to plating and painting. | Low – Medium | Very Easy | Consumer electronics housings, Lego bricks, automotive interior trim, appliance panels. |
| PP | Unmatched flexural fatigue resistance, excellent chemical resistance, very low density. | Very Low | Easy | Living hinge closures, microwave-safe containers, automotive bumpers. |
| PE | Outstanding moisture barrier and electrical insulation, excellent low-temperature toughness. | Very Low | Easy | Large industrial containers, trash bins, flexible bottle caps, household food storage. |
| PC | Bullet-resistant impact strength, extremely high optical clarity and heat resistance. | Medium – High | Moderate to Hard | Safety goggles, automotive headlamp lenses, transparent riot shields, medical devices. |
| POM (Acetal) | Extremely wear-resistant, inherent self-lubricity, high stiffness, and creep resistance. | Medium | Moderate to Hard | Precision gears, mechanical cams, sliding bearings, zipper teeth. |
| Nylon (PA) | Exceptionally high tensile strength and toughness, abrasion-resistant, withstands oil and solvents. | Medium | Moderate | Industrial cable ties, power tool housings, automotive under-hood components. |
| Acrylic (PMMA) | Ultimate optical clarity, outstanding outdoor UV and weather resistance. | Medium | Moderate | Automotive taillights, optical lenses, light guide panels, premium cosmetic packaging. |
| PEEK | Withstands extreme heat, ultra-high strength, inherently flame retardant. | Very High | Very Hard | Aerospace structural components, medical implants, semiconductor processing parts. |
| PET | Excellent gas and moisture barrier properties, high strength and rigidity, good dimensional stability. | Low – Medium | Moderate to Hard | Medical blood collection tubes, electrical connectors (glass-filled), high-strength precision parts. |
| PVC | Inherently flame retardant , excellent chemical and weather resistance. | Low | Very Hard | Construction pipe fittings, electrical insulation housings, medical oxygen masks (flexible) |
From the table above, you can see that the cost and processing difficulty are often proportional to the high performance of the materials.
Conclusion
The above are the 10 most suitable plastic materials for injection molding. In fact, material selection is just your first step. how to perfectly execute the design is the key to successfully launching a product to market. And our DSR company is a manufacturer that can perfectly implement your design solutions. Whether you need to quickly verify complex POM gears through CNC machining or need to injection mold thousands of ABS enclosures in large quantities, our manufacturing capabilities can meet your project needs. Send your CAD files now and let our team help you turn the most suitable plastic into the highest quality parts.
FAQ
Q1: What is the strongest plastic for injection molding?
A: PEEK is recognized as the plastic with the highest overall strength and most robust performance.
Q2: Is HDPE used in injection molding?
A: Yes. Common HDPE injection molded parts in your daily life include beverage bottle caps, household trash cans, food storage containers, and sturdy children’s toys, etc.
Q3: What is the cheapest plastic for injection molding?
A: PE materials, especially LDPE and HDPE.
Q4: Is HDPE more expensive than PVC?
A: Generally, PVC is often slightly cheaper than HDPE.
Q5: What is the disadvantage of HDPE?
A: Extremely high molding shrinkage, low heat resistance limit,extremely weak ultraviolet (UV) resistance.
Q6: Is PS plastic safe?
A: PS plastic is generally considered safe and approved by regulatory agencies such as the FDA. The material is now widely used in disposable tableware, cold drink cups and food packaging boxes.
Q7: What are the most widely used plastics for general-purpose injection molding?
A: PP (Polypropylene), PE (Polyethylene), ABS (Acrylonitrile Butadiene Styrene), and PS (Polystyrene).
Q8: Compare polypropylene vs ABS for injection molding applications?
A: PP has excellent fatigue resistance and chemical corrosion resistance. It is light weight and low cost, so the material is very suitable for food containers, medical washing parts and parts that require repeated bending. ABS has excellent structural rigidity, impact resistance and dimensional stability, so the material is very suitable for making components such as household appliance casings and consumer electronic panels.
Q9: What are the typical costs associated with popular injection molding materials?
A: The plastic materials at the economic level are PP and PE. Mid-layer plastics include ABS, PC and POM. High-end plastic materials are high-performance specialty polymers such as PEEK or PEI (Ultem).
Q10: What are the three unsafe plastics?
A: #3 PVC, #7 PC plastics and black plastics.
