The Common Plastics for Injection Molding

Plastic Injection molding is one of the most widely used manufacturing processes in the world, producing millions of plastic components every day. From automotive parts and medical devices to packaging and consumer goods, this process provides efficiency, precision, and scalability. However, one of the most important factors in ensuring the success of an injection molding project is choosing the right plastic material.

In this article, we’ll explore the common plastics for injection molding, their properties, applications, pros and cons, and how to select the best one for your project. By the end, you’ll have a clear understanding of which plastics are most commonly used in injection molding and why.

Why Material Choice Matters in Injection Molding

The plastic material you choose directly impacts:

• Product durability – Resistance to impact, wear, or environmental conditions.

• Cost-effectiveness – Some plastics are cheaper but may not meet high-performance requirements.

• Manufacturing efficiency – Certain plastics cool faster, reduce cycle time, and lower production costs.

• Compliance and safety – Industries like food packaging and medical devices require FDA-approved or biocompatible plastics.

Because of these factors, understanding the common plastics for injection molding is critical for manufacturers, engineers, and product designers.

The Most Common Plastics for Injection Molding

Let’s dive into the most widely used plastics in injection molding. These materials have proven reliability across industries due to their mechanical, thermal, and chemical properties.

1. Acrylonitrile Butadiene Styrene (ABS)

Overview: ABS is one of the most popular plastics for injection molding thanks to its balance of strength, toughness, and affordability.

Key Properties:

• High impact resistance

• Lightweight yet durable

• Excellent machinability

• Glossy surface finish

• Easily colored or painted

Applications:

• Automotive parts (dashboards, panels, trim components)

• Consumer electronics (computer keyboards, phone housings)

• Toys (famously used in LEGO bricks)

• Medical devices (non-implant applications)

Pros: Affordable, strong, versatile, and widely available.
Cons: Poor resistance to UV and weathering unless modified.

2. Polypropylene (PP)

Overview: Polypropylene is the most commonly used thermoplastic polymer in injection molding. Known for its flexibility and chemical resistance, it is widely applied in packaging and consumer goods.

Key Properties:

• Lightweight with high chemical resistance

• Excellent fatigue resistance (living hinges)

• Good impact strength at room temperature

• Cost-effective

Applications:

• Food containers and packaging

• Automotive bumpers and battery cases

• Caps, closures, and hinges

• Household goods

Pros: Inexpensive, versatile, resistant to moisture and chemicals.
Cons: Poor resistance to UV unless stabilized; low-temperature brittleness.

3. Polycarbonate (PC)

Overview: Polycarbonate is known for its transparency and high impact resistance, making it ideal for safety and optical applications.

Key Properties:

• High impact strength (250x stronger than glass)

• Excellent optical clarity

• Good dimensional stability

• Can be sterilized

Applications:

• Eyeglass lenses

• Safety helmets and protective gear

• Automotive headlamp lenses

• Electronic components

Pros: Extremely strong, transparent, and heat-resistant.
Cons: More expensive than ABS and prone to scratching.

4. Nylon (Polyamide, PA)

Overview: Nylon is a strong, wear-resistant plastic with excellent mechanical properties, often used as a metal substitute.

Key Properties:

• High tensile strength and toughness

• Resistance to abrasion and wear

• Can withstand high temperatures

• Good chemical resistance

Applications:

• Gears and bearings

• Automotive under-the-hood components

• Industrial machinery parts

• Sports equipment

Pros: Strong, lightweight, durable.
Cons: Absorbs moisture, which may affect dimensional stability.

5. Polyethylene (PE)

Overview: Polyethylene is one of the most versatile plastics for injection molding, available in different densities: LDPE, HDPE, and UHMWPE.

Key Properties:

• Excellent impact resistance

• High ductility and flexibility

• Chemical resistance

• Food-safe grades available

Applications:

• Food and beverage containers

• Toys and household items

• Pipes and fittings

• Packaging materials

Pros: Inexpensive, widely available, easy to process.
Cons: Lower strength compared to engineering plastics; poor UV resistance.

6. Polystyrene (PS)

Overview: Polystyrene is a rigid, low-cost plastic often used for disposable consumer products.

Key Properties:

• Lightweight and inexpensive

• Easy to mold with good dimensional stability

• Can be clear or opaque

Applications:

• Disposable cutlery and cups

• Packaging inserts

• CD cases

• Medical diagnostic components

Pros: Cheap, lightweight, easy to mold.
Cons: Brittle, poor resistance to heat and chemicals.

7. Polyethylene Terephthalate (PET)

Overview: PET is best known for its use in beverage bottles but is also injection molded for industrial applications.

Key Properties:

• High tensile strength

• Excellent chemical resistance

• Food-safe and recyclable

• Good dimensional stability

Applications:

• Beverage bottles and food containers

• Automotive parts

• Electrical components

Pros: Strong, recyclable, FDA-approved for food contact.
Cons: Sensitive to moisture during processing.

8. Polyoxymethylene (POM, Acetal)

Overview: Often referred to as acetal, POM is a high-performance engineering plastic ideal for precision components.

Key Properties:

• Low friction and high wear resistance

• Excellent dimensional stability

• High strength and stiffness

• Resistant to fuels and solvents

Applications:

• Gears, bearings, and fasteners

• Automotive fuel system components

• Consumer goods like zippers and buckles

Pros: Strong, durable, excellent for moving parts.
Cons: Sensitive to UV and acids.

9. Thermoplastic Elastomers (TPE)

Overview: TPE combines the characteristics of rubber and plastic, making it flexible and versatile.

Key Properties:

• Elastic, rubber-like flexibility

• Easy to mold and recycle

• Good grip and soft touch

Applications:

• Seals and gaskets

• Medical tubing

• Overmolded grips for tools

• Footwear

Pros: Flexible, recyclable, and versatile.
Cons: Less durable than true vulcanized rubber.

Comparison Table: Common Plastics for Injection Molding

Plastic	Strength	Flexibility	Heat Resistance	Cost	Common Uses
ABS	High	Medium	Medium	Low	Electronics, toys
PP	Medium	High	Low	Very Low	Packaging, automotive
PC	Very High	Low	High	Medium-High	Lenses, helmets
Nylon (PA)	High	Medium	High	Medium	Gears, auto parts
PE	Low-Medium	High	Low	Very Low	Containers, toys
PS	Low	Low	Low	Very Low	Disposable items
PET	Medium	Low	Medium	Low	Bottles, packaging
POM (Acetal)	High	Low	Medium	Medium	Gears, fuel systems
TPE	Medium	High	Low	Medium	Seals, grips

How to Choose the Right Plastic for Injection Molding

When selecting a plastic for injection molding, consider:

1. Mechanical Requirements – Does the product need high strength, flexibility, or wear resistance?

2. Environmental Exposure – Will it face UV, moisture, or chemicals?

3. Regulatory Needs – Does it need FDA or medical-grade approval?

4. Cost and Volume – Is it for mass production or specialized low-volume runs?

5. Aesthetic Considerations – Do you need a glossy finish, transparency, or vibrant colors?

Future Trends in Injection Molding Plastics

• Biodegradable plastics like PLA and PHA are gaining popularity due to environmental concerns.

• High-performance composites combining plastics with fibers for stronger, lighter products.

• Recycled plastics for sustainable manufacturing and circular economy practices.

Conclusion

Choosing the right material is the foundation of a successful injection molding project. While there are hundreds of plastics available, the most common plastics for injection molding—such as ABS, PP, PC, Nylon, PE, PS, PET, POM, and TPE—cover the majority of industrial and consumer applications.

Each material has its strengths and limitations, so the decision should be based on mechanical requirements, environmental conditions, cost, and compliance needs. With proper selection, injection molding can deliver products that are durable, cost-effective, and perfectly suited to their intended use.