Polyethylene (PE) is the most widely used plastic on the planet. If you look around your room right now, you are likely within arm’s reach of it. In the world of molding, we generally split the family into two distinct personalities: HDPE (the rigid, tough big brother) and LDPE (the flexible, soft little brother).
While they share the same DNA, their molecular structures are different. HDPE has straight chains that pack together tightly (high density), while LDPE has branched chains that keep things loose and flexible.
| Property | HDPE (High Density) | LDPE (Low Density) | Why it Matters |
| Density (g/cm³) | 0.94 – 0.97 | 0.91 – 0.94 | HDPE is heavier/sturdier; LDPE is lighter |
| Tensile Strength | 20 – 30 MPa | 8 – 15 MPa | HDPE handles more mechanical stress |
| Melting Point | ~130°C | ~110°C | HDPE stays rigid at higher temperatures |
| Flexibility | Rigid / Stiff | Highly Flexible | LDPE can be squeezed and bounced |
| Molding Shrinkage | 1.5% – 4.0% | 1.5% – 3.5% | Both have high shrinkage—tooling must adjust |
HDPE: The Industrial Strength Choice Because of its high “strength-to-density” ratio, HDPE is the king of Blow Molding. It’s the material behind milk jugs, bleach bottles, and fuel tanks. In Injection Molding, it’s used for items that need to take a beating, like heavy-duty crates, buckets, and outdoor toys.
LDPE: The “Squeeze” Specialist LDPE is all about tactile feel and impact absorption. In Blow Molding, it’s perfect for squeeze bottles (like honey or mustard containers) because it returns to its original shape after being pressed. In Injection Molding, it’s the go-to for snap-on lids and flexible dust caps that need to stretch slightly to fit.
The Bottom Line: Both materials are incredibly resistant to chemicals and moisture, and they are fully recyclable. However, they are difficult to “glue” or paint because their surfaces are so waxy and non-stick. If you need a part that survives a drop or holds liquid safely, the PE family is your best bet.
Are you designing a container for a chemical cleaner or a flexible lid for a food jar? I can help you decide if the rigidity of HDPE or the softness of LDPE fits your user experience better.
Contact us to evaluate manufacturability, tolerances, and cost for your specific application.
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