The beverage bottle in your hand, the laundry detergent container, even components inside your car—these everyday items may all be made from two common plastics: high-density polyethylene (HDPE) and polyethylene terephthalate (PET). While both materials are ubiquitous in modern life, they serve different purposes based on their distinct properties. This comprehensive comparison examines their characteristics, applications, costs, and recyclability to help manufacturers and consumers make informed choices.
HDPE: The Durable Workhorse
High-density polyethylene (HDPE) is a thermoplastic derived from petroleum byproducts. As a member of the polyethylene (PE) family, HDPE distinguishes itself through fewer side-chain branches, resulting in higher density and greater strength. This molecular structure—tightly packed and orderly arranged—gives HDPE superior durability compared to other plastics.
Often described as the "heavy lifter" of plastics, HDPE excels in applications requiring resistance to pressure and deformation. Its robustness makes it ideal for products subjected to heavy loads or frequent use, from household cleaning product containers to automotive components.
PET: The Versatile Performer
Polyethylene terephthalate (PET), another petroleum-derived polymer, serves as a true multitasker in the plastic world. Its adaptable nature allows it to function as textile fibers, food and beverage containers, packaging films, and even engineering plastics. The material's versatility stems from its molecular structure—repeating C10H8O4 units that can be processed to achieve different properties.
PET can exist in either transparent amorphous forms or semi-crystalline states, with crystallization enhancing its heat resistance and strength. Through biaxial stretching (during film production or blow molding), PET gains improved strength and clarity—a version commonly marketed as Mylar®.
Application Showdown: Distinct Strengths
HDPE Applications:
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Automotive:
Fuel tanks, wiring cables, cable ties, fasteners, body mounting clips
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Household Goods:
Trash bins, gardening equipment, furniture, storage containers, children's toys, playground equipment
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Packaging:
Crates, pallets, milk jugs, PET bottle caps, fuel cans, industrial liquid containers
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Textiles:
Ropes, fishing nets, sports nets, industrial and decorative fabrics
PET Applications:
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Beverage Packaging:
Water and carbonated drink containers
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Food Packaging:
Non-oriented films for thermoformed trays and blisters
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Industrial Uses:
Oriented PET films for magnetic tapes
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Household Items:
Product jars, heat-resistant/microwave-safe kitchen containers
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Textiles:
PET monofilament "felt" (non-woven fabrics for printing or oil/water separation)
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Automotive:
Wiper arms, gear housings, engine covers, connector housings (often glass-filled)
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Electronics:
Insulation components
Shared Applications:
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Liquid Containers:
Both offer excellent chemical resistance and low contamination risk
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Electrical Insulation:
Both demonstrate high dielectric breakdown voltages
Performance Comparison: By the Numbers
The following table provides a detailed comparison of physical properties between standard PET, biaxially oriented PET, and HDPE:
|
Property
|
PET (Metric)
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Biaxially Oriented PET (Metric)
|
HDPE (Metric)
|
|
Density
|
0.7–1.45 g/cm³ (typical 1.3 g/cm³)
|
1.39 g/cm³
|
0.933–1.27 g/cm³
|
|
Hardness (Shore D)
|
71–87
|
N/A for films
|
55–69
|
|
Tensile Strength (Ultimate)
|
22–95 MPa
|
20 (MD)–24 (XMD) MPa
|
15.2–45 MPa
|
|
Tensile Strength (Yield)
|
55–260 MPa
|
200 MPa
|
2.69–200 MPa
|
|
Elongation at Break
|
4–600%
|
110%
|
3–1900%
|
|
Elastic Modulus
|
1.57–5.2 GPa
|
5.2 (MD)–5.5 (XMD) GPa
|
0.483–1.45 GPa
|
|
Flexural Yield Strength
|
55.1–135 MPa
|
—
|
16.5–91 MPa
|
|
Flexural Modulus
|
0.138–3.5 GPa
|
4.1–4.3 GPa
|
0.5–4.83 GPa
|
|
Dielectric Constant
|
2.4–3.7
|
—
|
2.0–2.6
|
|
Melting Point
|
200–260°C
|
254°C
|
120–130°C
|
|
Maximum Service Temperature
|
60–225°C
|
121°C
|
80–120°C
|
MD: Machine direction stretching, XMD: Cross-machine direction stretching
Recycling Realities: Environmental Impact
While both HDPE and PET are technically recyclable, their actual recycling rates remain disappointingly low. HDPE can undergo multiple recycling cycles, but most still ends up in landfills, incinerators, or the natural environment. PET benefits from easier sorting due to its widespread use in beverage bottles, making it one of the few polymers with potential for circular supply chains. Nevertheless, the majority of PET waste still meets the same fate as HDPE—burned, buried, or polluting ecosystems.
Cost Considerations: Economic Factors
HDPE represents a low-cost commodity material, with virgin resin priced around $8.50/kg and recycled material at $2.50/kg. PET also falls into the affordable commodity category but spans a wider quality range. Basic, non-branded pellets cost $0.80–2.00/kg, while branded materials like DuPont® command $2.00–3.00/kg. Recycled PET typically sells for $0.80–1.20/kg.
Alternative Materials: Exploring Options
HDPE's relatively narrow application scope makes its alternatives more straightforward, including LDPE, PEX, ABS, PP, and rubber-modified PP. PET's dominance in single-use packaging has spurred searches for environmentally friendlier substitutes:
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Bio-based:
PEF, PET, PE, PA, and PTT
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Biodegradable:
PCL and PBAT
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Bio-based & Biodegradable:
PBAF, PLA, PHA, PBS, and starch-based materials
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Fiber Alternatives:
Nylon, polyester, cotton, linen, and hemp
Making the Right Choice
Both HDPE and PET offer valuable properties for different applications. HDPE excels in durability and impact resistance, while PET provides superior clarity, strength, and heat tolerance. The optimal choice depends on specific product requirements, budget constraints, and environmental considerations. By understanding these materials' fundamental differences, manufacturers and consumers can make decisions that balance performance, cost, and sustainability.
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