Injection Molding is one of the most widely used manufacturing processes for creating plastic parts in large volume. Its success depends heavily on selecting the right plastic resin. Among a multitude of available polymers, one resin stands out for its frequency of use across industries. This article explores which plastic is the most common in injection molding, why it enjoys this status, what its advantages and limitations are, and how to choose among alternatives. Toward the end, I also briefly introduce BOHANG and how it may be relevant if you’re involved in plastic processing or equipment.

The Most Common Plastic in Injection Molding

While there is no single polymer that dominates 100 % of applications, polypropylene (PP) is widely regarded as the most commonly used resin in injection molding. Many industry sources list PP at or near the top of the use-share for general-purpose molded parts.

Another strong contender is acrylonitrile butadiene styrene (ABS), especially in consumer goods, electronics housings, and components requiring a balance of strength and aesthetics.

In summary:

• Polypropylene is often the go-to for generic, high-volume parts.

• ABS is also very popular where toughness and surface finish matter.

Let’s dig deeper into why PP is so common, and when ABS or others might instead be preferable.

Why Polypropylene (PP) Is So Common

1. Affordability and Availability

PP is relatively inexpensive compared to many engineering resins. Supply chains are robust, and many grades and formulations exist.

2. Good Balance of Properties

PP offers a favorable set of physical properties:

• Good chemical resistance (resists many acids, bases, solvents)

• Decent impact strength

• Fair fatigue resistance (especially useful for living hinges)

• Low density (lightweight parts)

These characteristics make it suitable for many general-purpose parts.

PP is also commonly used for monobloc chairs (single-piece molded plastic chairs) as an example of how it can be molded into large, thin-walled shapes in high volume.

3. Processability in Injection Molding

PP exhibits favorable flow behavior, relatively lower melt viscosity, and good mold filling characteristics when designed properly. It can often be injection molded without exotic equipment or extreme conditions.

It also tolerates a wide processing window, making it forgiving for many injection molders.

4. Design Flexibility (Living Hinges, Thin Walls)

One hallmark of PP is its ability to form living hinges (thin sections that flex repeatedly without failure). Because PP can handle cyclic bending and fatigue, it is used in snap-fit closures, flip lids, and other features where repeated bending is needed.

Because PP’s stiffness is moderate, it also allows parts to be designed with thin walls, reducing material usage, weight, and cycle time.

Strengths and Limitations of PP

Strengths

• Low cost per kilogram

• Low density → lightweight parts

• Good chemical resistance

• Good fatigue strength (especially for living hinges)

• Wide processing window

• Easily available grades, filled or reinforced

Limitations

• Moderate heat resistance (not suitable for high-temperature or load-bearing structural applications)

• Poor resistance to UV or prolonged sunlight unless stabilized

• Lower stiffness compared to some engineering plastics

• Not ideal in cases where premium surface finish, dimensional stability, or high mechanical performance is required

ABS and Other Common Resins

Because PP does not cover every application, many molders turn to other plastics depending on performance demands.

ABS (Acrylonitrile Butadiene Styrene)

ABS is frequently used in housings, consumer electronics, toys (e.g. LEGO bricks), and structural parts. It offers higher toughness, good surface finish, and better dimensional stability.

ABS is a good compromise between cost and performance, especially when aesthetics (texture, paintability) matter.

Other Plastics Common in Injection Molding

Here are a few others that are commonly used alongside PP and ABS:

The best choice always depends on the part’s functional requirements, processing restraints, cost constraints, and durability expectations.

Choosing the Right Plastic for a Project

When selecting a plastic resin for injection molding, consider the following factors:

1. Mechanical Requirements Tensile strength, stiffness, impact resistance, fatigue, wear, etc.

2. Thermal Requirements Operating temperature, heat deflection, proximity to heat sources.

3. Chemical and Environmental Resistance Exposure to solvents, UV, moisture, chemicals, or outdoor conditions.

4. Aesthetic and Surface Quality Need for gloss, texture, paint adhesion, color stability.

5. Cost Constraints Material cost, ease of molding, cycle time, scrap rate, tooling.

6. Moldability Flowability, shrinkage, warpage, design for manufacturability.

Often engineers run trade-studies or prototypes with multiple candidate resins.

BOHANG and Its Relevance

If your business involves plastics, molds, or molding equipment, BOHANG is one of the manufacturers you may come across. BOHANG specializes in various machines such as Bottle Blowing Machines and related equipment.

While BOHANG may not be a resin supplier, if your operation spans both plastic molding and auxiliary equipment (like drying, conveying, or blow molding), integrating BOHANG machinery can help streamline production. Choosing the right upstream equipment (like dryers, feeders, mold temperature controllers) is just as critical as selecting the correct resin for injection molding.

Conclusion

In injection molding, polypropylene (PP) often holds the crown as the most commonly used plastic resin, thanks to its affordability, balanced performance, and ease of processing. However, ABS, nylon, polycarbonate, POM, and others have strong roles in specialized applications where additional strength, better aesthetics, thermal resistance, or wear properties are required.

When selecting a material, always weigh mechanical, thermal, chemical, aesthetic, cost, and moldability factors. And if you’re also sourcing processing or auxiliary equipment, BOHANG is one of the names you can explore for machinery support.