HDPE (High-Density Polyethylene)

HDPE is produced with very little branching along its polymer backbone, typically through Ziegler-Natta or chromium-based catalysts, which lets the molecular chains pack tightly together. That tight packing produces a density generally between 0.941 and 0.965 grams per cubic centimeter and a much higher degree of crystallinity than LDPE or LLDPE. In film form, this translates into a stiffer, less stretchy material with a distinctive crinkly or papery hand feel that most people recognize from grocery store t-shirt bags.

HDPE film offers excellent moisture barrier and good stiffness at very low gauges, which makes it economical for high-volume, lightweight applications like retail merchandise bags, bread bags, and some liner applications where rigidity rather than stretch is desired. Its higher crystallinity also tends to produce more haze and lower clarity than LLDPE or LDPE, and its lower elongation makes it more prone to tearing rather than stretching under stress, so it's rarely used alone where puncture resistance is the top priority.

In blown film, HDPE is often run at very thin gauges, sometimes under one mil, since its stiffness allows a usable bag to be made with very little material, which is part of why it remains a cost-efficient choice in high-volume retail and grocery bag production.

The crinkly, slightly rattly bag handed out at a retail checkout counter is almost always HDPE, chosen because it lets the bag manufacturer use very little resin per bag while still getting a serviceable, stiff carrying bag.

It is a common misconception that HDPE is simply a stronger, more durable version of LDPE or LLDPE because the name implies higher density equals higher quality. In film applications, HDPE actually has lower elongation and puncture resistance than LLDPE; its advantage is stiffness and moisture barrier at minimal gauge, not overall toughness.