Polyethylene is the most widely used plastic in the world and the one most often bought wrongly. Buyers order by family name, receive material that will not run properly on their line, and conclude the supplier sent the wrong thing. Usually the supplier sent exactly what was asked for. The specification was the problem.
The three families
| Family | Character | Typically used for |
|---|---|---|
| HDPE | High density, stiff, strong, good chemical resistance | Pressure pipe, blow moulded containers, crates and caps, heavy duty film, monofilament |
| MDPE | Medium density, between the two, good toughness | Rotational moulding, tanks, some pipe and film applications |
| LDPE | Low density, soft, flexible, clear | Packaging film, bags, sheeting, agricultural film, lamination |
The two numbers that decide everything
Beyond the family name, two properties do most of the work.
- Density, which broadly tracks stiffness and strength. Higher density means a more rigid, stronger part with better chemical resistance and less clarity.
- Melt flow index, which describes how easily the molten polymer flows. A high MFI flows readily and suits injection moulding of thin sections. A low MFI is more viscous and suits extrusion, pipe and film, where melt strength matters.
This is why a grade is described as, for example, a film grade or an injection grade. It is not marketing language. It is a statement about whether the material will behave on your process.
Matching the grade to the process
- Film extrusion needs melt strength to hold a bubble, so film grades sit at the lower end of the flow range
- Injection moulding needs the melt to fill a cavity quickly, so injection grades flow more freely
- Blow moulding needs enough melt strength to hold a parison without it thinning or dropping
- Pipe needs long-term pressure performance, which is why pipe material is classified as PE80 or PE100 rather than by flow alone
- Rotational moulding needs a powder that flows and fuses evenly at relatively low shear
What about UV stabilisation
Grades marked UA or UV carry ultraviolet stabiliser. If the finished part will sit in sunlight, a water tank, an outdoor moulding, agricultural film, it needs one. Unstabilised polyethylene degrades and becomes brittle in service, and it will not be obvious for months.
We supply HDPE, LDPE and MDPE across the processing range from Iranian producers, delivered by road across the Rimdan border. If you tell us the process and the part rather than just a grade code, we can confirm whether the grade you are asking for is the one you actually want.
Need this applied to your shipment?
General guidance only gets you so far. Send us the product, the quantity and the destination and we will tell you exactly how it works for your case, including the numbers.