HDPE (High-Density Polyethylene): chemically resistant and lightweight

HDPE stands for high-density polyethylene, the rigid and strong variant of polyethylene. It is lightweight, virtually insensitive to moisture and resistant to acids, alkalis, oils and most solvents. You will find it in crates, jerry cans, pipes and household items. The material stays tough well below zero, where many other plastics become brittle. QDP chooses HDPE for parts that must resist chemicals or frost.

They are similar and in the same price range. HDPE is tougher at low temperatures and remains impact resistant even with frost, PP is stiffer and withstands higher temperatures. HDPE also shrinks more, up to 3 percent, which makes dimensional stability more difficult. For a crate that sits outside in winter, you choose HDPE; for a stiff part that gets warm, PP. QDP chooses based on the actual load, not habit.

Mainly for functional, robust parts: crates and containers, caps and closures, fittings and pipe parts, components for agriculture and construction, and packaging that must withstand aggressive contents. The surface is matte and waxy, so it is not a material for visible parts with a high-gloss finish. Where strength, chemical resistance and price count, HDPE stands out. QDP assesses during design if it is the right choice.

HDPE is odorless and tasteless and contains no plasticizers, which is why it is widely used in food packaging and kitchenware. Food-grade, however, is not a property of the plastic itself but of the specific grade, including pigment and additives, with a declaration of conformity according to the European regulation. Always request this certificate with the chosen material. QDP arranges this declaration per project as soon as food contact is required.

Gluing works poorly, just as with PP, because of the low surface energy: without pre-treatment, almost no glue will adhere. Welding, on the other hand, works excellently and is the usual route for HDPE constructions. For an injection-molded product, a snap or screw connection is usually the simplest solution, as it is included in the mold and requires no extra step. QDP makes that choice during the design, not afterward.

HDPE shrinks around 1.5 to 3 percent, the highest among the commonly used injection molding plastics. This requires consistent wall thickness, wider tolerances and attention to warping in large surfaces. The mold is built for that shrinkage, so the material is fixed as soon as the steel is there and changing it later means a new mold. QDP calculates the shrinkage per product in the mold dimension.