HDPE Plastic: Key Benefits and Applications
A strong, lightweight plastic with excellent chemical resistance, HDPE is a reliable material for both machined and molded parts.
What is HDPE?
| High-Density Polyethylene (HDPE) is a thermoplastic known for its high strength-to-weight ratio, excellent durability, and ease of use in manufacturing. It’s lightweight and flexible, making it a staple in both industrial and consumer manufacturing. Due to its low moisture absorption and food-safe grades, HDPE is a go-to choice for fluid-handling systems and components in food and medical applications. |
Protolabs HDPE Capabilities
Protolabs offers HDPE for both CNC machining and injection molding, with the following capabilities:
HDPE for Injection Molding
Injection molding is ideal for producing HDPE parts at scale, especially when consistent geometry and regulatory compliance are required.
| Best for | High volumes. Produce end-use parts at scale. |
| Tolerance | Typically ~0.009 in./in. Note that HDPE's high shrink rate (~0.020 in./in.) may impact precision. |
| Shrinkage | Requires thoughtful part design—uniform wall thickness and draft angles are key to maintaining accuracy. |
| Wall thickness | Minimum recommended is 1.5 mm to avoid warping or sink marks. |
| Color options | We offer a wide range of colorants, with customization available. |
| Surface finish | Generally smooth, but may vary depending on geometry and mold quality. |
| Data sheets | Dow DMDA 8907 NT7 Marlex 9006 |
HDPE for CNC Machining
CNC machining is great for quick-turn prototyping and low-volume production using HDPE.
| Best for | Prototypes and low-volume parts. Fast turnaround with good dimensional control. |
| Tolerance | Aligns with ISO 2768-medium unless otherwise specified. |
| Wall thickness | Can accommodate thinner walls than injection molding depending on part geometry, though strength and accuracy may vary. |
| Color options | Available in black and natural; natural is FDA-approved in EMEA. Additional options are available on request. |
| Surface finish | Typically milled and matte, depending on toolpath and speed. |
| Flexibility considerations | Parts may require fixturing due to HDPE’s softness. |
| Data sheets | HDPE |
Manufacturing with HDPE
| HDPE is a versatile material, but the way it behaves in production depends heavily on the process you choose. From shrinkage in molding to support requirements in machining, knowing what to expect helps ensure you get the performance you need. |
CNC Machining with HDPE
CNC machining is best for quick-turn prototypes or low-volume HDPE parts that don’t require mold investment. It’s great for fast design iterations—just keep in mind that HDPE’s softness can affect finish quality and fixturing.
Design Guidelines
- Avoid overly thin or flexible geometries—HDPE can deflect under machining pressure
- Provide extra fixturing or support features for long, unsupported sections
- Use generous radii and avoid sharp internal corners to improve machinability
- Consider surface finishing needs—HDPE’s softness means visible tool marks are common
Injection Molding with HDPE
When it’s time to scale up, injection molding offers consistent part geometry, regulatory compliance, and efficient production for HDPE parts. The process supports higher volumes and tighter repeatability, but it requires careful design to manage shrinkage.
Design Guidelines
- Use draft angles of at least 1° per side to ensure easy part release from the mold
- Maintain uniform wall thickness (min. 1.5 mm) to reduce internal stress and warping
- Avoid thick sections that can cause sink or increased shrinkage
- Add fillets instead of sharp corners to improve flow and reduce stress
Advantages and Disadvantages of HDPE
Advantages
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Disadvantages
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HDPE Compared to Other Thermoplastics
| HDPE shares many properties with other thermoplastics, but each comes with its own trade-offs. Here’s a side-by-side look at how common alternatives stack up when it comes to flexibility, durability, chemical resistance, and more: |
| Material | Flexibility | Durability | Temp. Range | Chem. Resist. | Common Uses | Pros | Cons |
|---|---|---|---|---|---|---|---|
| HDPE | Moderate | High | ~130°C | Excellent | Medical, auto, food | Light, FDA-safe, tough, chem. resistant | Shrinks (IM), low stiffness, hard to bond |
| LDPE | High | Moderate | ~105°C | Excellent | Packaging, tubing, liners | Very flexible, good chem. resistance | Less stable than HDPE |
| PP | Mod-High | Mod-High | ~100°C | Excellent | Consumer, auto, medical | Fatigue-proof, inert | Brittle in cold, tricky to bond |
| Acetal (POM) | Low | High | ~180°C | Good | Auto, industrial, consumer | Rigid, dimensionally stable | Costly, not acid-safe |
| Nylon (PA) | Moderate | High | ~180°C | Moderate | Auto, industrial, robotics | Strong, wear-proof, heat-tolerant | Absorbs water, affects function |
| ABS | Moderate | Moderate | ~100°C | Fair | Consumer, electronics, toys | Strong, machinable, easy to finish | Low UV resistance, limited chem. resistance |
- LDPE: More flexible but less stiff and less dimensionally stable than HDPE
- PP (Polypropylene): Better fatigue resistance, similar chemical profile, more rigid
- Acetal (POM): Higher stiffness and dimensional stability, but more expensive
- Nylon (PA): Higher strength and thermal resistance, but absorbs more moisture
- ABS: Easier to machine and finish than HDPE, but less chemically resistant and not ideal for outdoor use
Applications
HDPE is used across industries for parts that require toughness, low weight, and chemical resistance:
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