Plastic Resin Identification Codes: Complete Guide to Codes 1-7

A procurement manager at a mid-sized packaging company once ordered 20 metric tons of what the supplier labeled "general-purpose polyethylene." The material arrived, the pellets looked right, and production started. Two weeks later, the molded containers began cracking under moderate stress. The culprit? The supplier had shipped LDPE (Code 4) instead of HDPE (Code 2). Same family, vastly different performance. That mistake cost the company over $40,000 in scrapped product and a missed delivery window.

Plastic resin identification codes exist precisely to prevent this kind of error. These small numbered triangles stamped on plastic products tell you exactly which polymer family you are working with. For engineers, procurement professionals, and manufacturers, understanding these codes is not optional; it is fundamental to material selection, quality control, and regulatory compliance.

This guide covers all seven plastic resin identification codes, explains what each code means for your applications, and shows how to use this knowledge to make better sourcing and processing decisions.

What Are Plastic Resin Identification Codes?

Plastic resin identification codes are the numbering system developed by the Society of the Plastics Industry (SPI) in 1988 to classify the seven most commonly used thermoplastic resins. You recognize them as the triangular arrows symbol with a number from 1 to 7 inside, usually stamped on the bottom of plastic products.

The resin identification system was originally created to help recycling facilities sort plastics by polymer type. However, for manufacturers and engineers, these codes serve a far more important function: they provide an immediate, standardized way to identify the base polymer of any plastic component or raw material.

Each code corresponds to a specific polymer family with distinct mechanical, thermal, and chemical properties. Knowing the code tells you how the material will behave during processing, how it performs in service, and what recycling stream it belongs to.

Important Note: The resin identification code identifies the polymer family only. It does not specify grade, fillers, additives, or exact formulation. A Code 7 (Other) could be polycarbonate, ABS, or nylon. Always request a Technical Data Sheet (TDS) for detailed grade specifications.

Why the Resin Identification System Matters for Manufacturers

For manufacturing professionals, the resin identification system matters in three critical ways:

Material Selection: Understanding what each code represents helps you narrow down polymer candidates for your application before diving into specific grade comparisons.

Quality Control: Incoming material verification starts with confirming the resin code matches the specification. A Code 2 material arriving when Code 5 was ordered indicates a serious supply chain error.

Regulatory Compliance: Many industries require specific resin codes for food contact, medical, or automotive applications. Knowing the codes ensures you specify compliant materials from the start.

The 7 Plastic Resin Identification Codes Explained

Code 1: PET (Polyethylene Terephthalate)

Polymer Type: Polyethylene Terephthalate (PET or PETE)

Common Applications: Beverage bottles, food packaging, polyester fibers, thermoformed containers

Key Properties:

• Tensile strength: 55-75 MPa

• Heat deflection temperature: 65-80°C at 1.8 MPa

• Density: 1.38 g/cm³

• Excellent clarity and gas barrier properties

• Good chemical resistance to dilute acids, oils, and alcohols

Processing: PET processes through injection molding and extrusion with melt temperatures of 260-280°C. It requires thorough drying (moisture below 0.02%) before processing to prevent hydrolytic degradation.

What Code 1 Means for Your Application: PET is the go-to polymer for transparent packaging requiring good barrier properties. In injection molding, it produces clear, stiff parts with good dimensional stability. However, its relatively low heat deflection temperature limits its use in applications exposed to sustained temperatures above 70°C.

Code 2: HDPE (High-Density Polyethylene)

Polymer Type: High-Density Polyethylene (HDPE)

Common Applications: Bottles, pipes, containers, fuel tanks, plastic lumber, geomembranes

Key Properties:

• Tensile strength: 22-31 MPa

• Heat deflection temperature: 60-80°C at 0.46 MPa

• Density: 0.941-0.965 g/cm³

• Excellent chemical resistance

• Good impact strength even at low temperatures

• Low moisture absorption

Processing: HDPE processes readily through injection molding, blow molding, and extrusion. Melt temperatures range from 180-240°C. It has a wide processing window and low shrinkage (1.5-3.5%), making it forgiving for mold designers.

What Code 2 Means for Your Application: HDPE is one of the most versatile engineering plastics available. Its combination of chemical resistance, stiffness, and processability makes it suitable for industrial containers, piping systems, and structural components. When you see Code 2, you know the material will resist most chemicals and offer good long-term durability. Shanghai Wenqin Plastics supplies HDPE grades suitable for injection molding and extrusion applications requiring consistent melt flow and reliable mechanical properties.

Code 3: PVC (Polyvinyl Chloride)

Polymer Type: Polyvinyl Chloride (PVC)

Common Applications: Pipes, window profiles, cable insulation, flooring, medical tubing

Key Properties:

• Tensile strength: 40-60 MPa (rigid PVC)

• Heat deflection temperature: 60-80°C (rigid PVC)

• Density: 1.30-1.45 g/cm³

• Self-extinguishing (inherent flame resistance)

• Good chemical resistance

• Excellent weatherability when properly formulated

Processing: PVC requires careful processing due to its thermal sensitivity. Rigid PVC processes at 160-200°C, while plasticized PVC (flexible PVC) processes at lower temperatures. Thermal degradation releases hydrogen chloride, requiring corrosion-resistant equipment and proper ventilation.

What Code 3 Means for Your Application: Rigid PVC offers excellent stiffness and flame resistance at low cost, making it dominant in construction applications. Flexible PVC (with plasticizers) provides versatility for cable insulation and tubing. However, PVC processing demands more attention to thermal stability than polyolefins, and the material's environmental profile has led some manufacturers to seek alternatives for certain applications.

Code 4: LDPE (Low-Density Polyethylene)

Polymer Type: Low-Density Polyethylene (LDPE)

Common Applications: Film and sheet, plastic bags, squeeze bottles, wire and cable insulation, coatings

Key Properties:

• Tensile strength: 8-15 MPa

• Heat deflection temperature: 40-50°C at 0.46 MPa

• Density: 0.910-0.940 g/cm³

• Excellent flexibility and toughness

• Good chemical resistance

• Low moisture absorption

Processing: LDPE processes easily through film blowing, extrusion coating, and injection molding. Melt temperatures range from 180-240°C. Its high melt flow and low viscosity make it excellent for thin-walled parts and film applications.

What Code 4 Means for Your Application: LDPE is the flexible cousin of HDPE. When you need a material that bends without breaking, resists moisture, and processes easily, LDPE fits the bill. Its lower density and softer nature make it unsuitable for structural applications, but it excels in packaging films, squeeze containers, and wire insulation where flexibility matters more than stiffness.

Code 5: PP (Polypropylene)

Polymer Type: Polypropylene (PP)

Common Applications: Automotive parts, food containers, medical devices, appliance housings, fibers

Key Properties:

• Tensile strength: 25-40 MPa

• Heat deflection temperature: 90-120°C at 0.46 MPa

• Density: 0.895-0.920 g/cm³ (lightest common engineering plastic)

• Excellent chemical resistance

• Good fatigue resistance (living hinge capability)

• Higher heat resistance than PE

Processing: PP processes through injection molding, blow molding, and extrusion with melt temperatures of 200-280°C. Shrinkage ranges from 1.0-2.5%, and the material has a relatively narrow processing window compared to polyethylene.

What Code 5 Means for Your Application: PP delivers the best heat resistance among commodity polyolefins, making it suitable for applications that see temperatures up to 100-120°C. Its excellent fatigue resistance enables living hinge designs in containers and caps. For automotive applications, glass-filled PP grades (PP GF20, PP GF30) compete with engineering plastics in many under-hood components at lower cost.

Code 6: PS (Polystyrene)

Polymer Type: Polystyrene (PS)

Common Applications: Disposable cutlery, packaging foam (EPS), CD cases, laboratory ware, insulation

Key Properties:

• Tensile strength: 35-55 MPa

• Heat deflection temperature: 65-95°C at 0.46 MPa

• Density: 1.04-1.10 g/cm³

• Excellent clarity (crystal PS)

• Good dimensional stability

• Brittle (poor impact resistance in standard grades)

Processing: PS processes easily through injection molding and extrusion with melt temperatures of 180-260°C. Low shrinkage (0.3-0.6%) and good flow make it suitable for thin-walled, detailed parts.

What Code 6 Means for Your Application: Standard polystyrene is stiff, clear, and inexpensive, but its brittleness limits engineering applications. High-impact polystyrene (HIPS) adds rubber modification for improved toughness at the cost of clarity. Expanded polystyrene (EPS) dominates packaging and insulation. For structural or high-impact requirements, engineers typically move to ABS (Code 7) or other engineering plastics.

Code 7: Other (All Other Plastics)

Polymer Type: Includes polycarbonate (PC), ABS, nylon (PA6, PA66), POM, PMMA, PBT, and all other thermoplastics not classified under Codes 1-6

Common Applications: Varies widely depending on specific polymer

Key Properties: Code 7 is a catch-all category. The properties depend entirely on the specific polymer:

• Polycarbonate (PC): Exceptional impact strength, transparency, heat resistance (HDT ~130°C)

• ABS: Good balance of impact, stiffness, and surface finish

• Nylon (PA6, PA66): High strength, wear resistance, chemical resistance

• POM (Acetal): Low friction, excellent fatigue resistance, dimensional stability

• PMMA (Acrylic): Optical clarity, UV resistance, weatherability

What Code 7 Means for Your Application: When you see Code 7, you cannot determine the material's performance characteristics without additional information. This is where the resin identification code system has its limits. Code 7 covers the entire range of engineering and high-performance plastics, each with distinct properties. Always request the specific polymer type and grade designation when Code 7 materials are involved.

Resin Identification Codes vs. Recyclability

A common misconception is that the resin identification code indicates recyclability. The codes identify the polymer type, not whether a specific item can be recycled in your local program. Recycling acceptance depends on:

• Local recycling infrastructure and capabilities

• Contamination levels and material cleanliness

• Additive packages and multi-material constructions

• Market demand for recycled resin

Codes 1 (PET) and 2 (HDPE) have the highest recycling rates globally due to established collection and reprocessing infrastructure. Codes 3-7 have varying recycling rates depending on region and application.

For manufacturers designing products with end-of-life considerations, understanding the resin identification system helps you specify materials that align with circular economy goals. Choosing a single-polymer design over multi-material construction simplifies recycling regardless of the specific code.

Common Mistakes When Using Resin Identification Codes

Mistake 1: Assuming Code Identifies Grade

The resin code tells you the polymer family, nothing more. Two materials both stamped Code 5 (PP) can have vastly different properties depending on whether they are homopolymer or copolymer, filled or unfilled, heat-stabilized or standard.

How to avoid it: Always request the full grade designation and Technical Data Sheet. The resin code is a starting point, not a specification.

Mistake 2: Confusing HDPE (Code 2) and LDPE (Code 4)

Both are polyethylene, but their density difference creates significantly different mechanical properties. HDPE is stiffer, stronger, and more heat resistant. LDPE is more flexible and has better stress-crack resistance.

How to avoid it: Never substitute one for the other without evaluating mechanical requirements. As the opening example illustrated, this mistake can be costly.

Mistake 3: Treating Code 7 as a Single Material

Code 7 encompasses dozens of different polymer families. Specifying "Code 7 material" without identifying the specific polymer is like ordering "food" at a restaurant without choosing a dish.

How to avoid it: Always specify the exact polymer type (PC, ABS, PA66, etc.) when working with Code 7 materials. Request grade-specific documentation.

Mistake 4: Ignoring Additives and Fillers

The resin code identifies the base polymer only. Glass fiber reinforcement, flame retardants, UV stabilizers, colorants, and other additives dramatically affect performance. A glass-filled PP (Code 5) behaves very differently from unfilled PP.

How to avoid it: Treat the resin code as one data point among many. Always review the complete material specification including filler content, additive packages, and test data.

How Shanghai Wenqin Plastics Supports Your Material Selection

Understanding plastic resin identification codes is the first step in material selection. The next step is matching the right grade to your specific application requirements.

At Shanghai Wenqin Plastics, we supply engineering plastics across multiple resin code categories, including ABS (Code 7), PC (Code 7), PP (Code 5), PE (Codes 2 and 4), PA6 and PA66 (Code 7), POM (Code 7), PBT (Code 7), and PMMA (Code 7). Our technical team provides material selection guidance that goes beyond the resin code to match grade properties, processing characteristics, and application requirements.

Need help selecting the right resin grade for your application? [Contact our technical team] for material recommendations tailored to your specific requirements, or [request a quotation] for competitive pricing on engineering plastics.

Resin Identification Codes Quick Reference

Frequently Asked Questions

What do the numbers inside the recycling triangle mean?

The numbers 1-7 inside the triangular arrows are plastic resin identification codes. Each number corresponds to a specific polymer family: 1 is PET, 2 is HDPE, 3 is PVC, 4 is LDPE, 5 is PP, 6 is PS, and 7 covers all other plastics including engineering polymers like PC, ABS, and nylon.

Is Code 7 plastic safe?

Code 7 is a catch-all category that includes many different polymers. Safety depends on the specific polymer and its intended use. For example, polycarbonate (a Code 7 material) is widely used in food-contact applications, while other Code 7 materials may not be suitable. Always verify the specific polymer type and its regulatory compliance for your application.

What is the difference between resin codes and recycling codes?

These terms are used interchangeably. The official name is the "Resin Identification Code" (RIC), but many people call them recycling codes or recycling numbers because the system was designed to help recycling facilities sort plastics. The ASTM D7611 standard governs the current version of this coding system.

Can two items with the same resin code have different properties?

Yes, absolutely. The resin code identifies only the polymer family, not the specific grade. Within each code, there are dozens or hundreds of different formulations with varying molecular weight, additives, fillers, and processing characteristics. Always request grade-specific technical data for critical applications.

Which resin codes are food-safe?

Several polymers across different codes have FDA-approved food-contact grades: PET (Code 1), HDPE (Code 2), PP (Code 5), and certain Code 7 materials like polycarbonate and specific nylon grades. However, food safety depends on the specific grade formulation, not just the base polymer. Always verify food-contact compliance documentation for the specific grade you intend to use.

Conclusion

Plastic resin identification codes provide a standardized starting point for understanding what polymer you are working with. Codes 1 through 7 cover the spectrum from commodity packaging plastics to high-performance engineering polymers. For manufacturers and engineers, these codes serve as a quick-reference system for material identification, quality verification, and initial screening.

However, the resin code is only the beginning. Selecting the right material for your application requires understanding specific grade properties, processing requirements, and compliance needs that go far beyond a number inside a triangle. Whether you need HDPE for chemical-resistant containers, PP for heat-resistant automotive components, or PC for impact-resistant housings, the key is matching the right grade to your specific requirements.

Shanghai Wenqin Plastics supplies a comprehensive range of engineering plastics with complete technical documentation, batch-tested quality, and expert material selection support. [Explore our product range] to find the right grade for your next project, or [contact our technical team] to discuss your application requirements.