High-Density Polyethylene

HDPE is linear polyethylene with minimal chain branching. That linearity produces higher crystallinity, stiffness, and chemical resistance than LDPE. Bottles are extrusion blow molded and closures are injection molded.

It is naturally a translucent white. Any color on an HDPE bottle is pigment, and pigment loading affects both wall appearance and, at high loadings, stress crack resistance.

• Chemical resistance: Excellent. Handles acids, bases, alcohols, and most solvents at ambient temperature. The default choice for aggressive fills.
• Moisture barrier: Very good, better than PET.
• Gas barrier: Poor. If oxygen ingress matters, HDPE is the wrong resin.
• Clarity: None. Translucent at best.
• ESCR: Environmental stress crack resistance is grade-dependent and matters for surfactant-bearing fills. Detergents and shampoos will crack a low-ESCR grade. Specify the fill before we specify the resin.

Shampoos, conditioners, and lotions. Industrial and agricultural chemicals. Supplement and nutraceutical packaging. Cannabis child-resistant jars where opacity doubles as UV protection.

Process: Extrusion blow molding for bottles, injection molding for closures. We run 3 PE blow molding lines and 21 injection machines.

Shrinkage: 1.5-3.0%, and anisotropic. It shrinks differently along the flow direction than across it, so tooling has to compensate. HDPE molds cannot simply be scaled from a PET design.

Parting line: EBM produces flash at the parting line and a pinch-off at the base. Both are trimmed in-line. Pinch-off weld strength is the most common EBM failure point, showing up as base splitting under drop test.

Draft: 1-2° minimum. Watch for sink marks on thick closure sections.