High-density polyethylene (HDPE) is one of the most versatile commodity resins, but "HDPE" alone tells you very little. The grade - defined mainly by melt flow index (MFI) and density - determines whether the material will run cleanly on your line and perform in the finished part. Here is a practical way to narrow it down.
Start with the process
Different conversion processes need different flow characteristics:
- Blow moulding (bottles, jerry cans): lower MFI for melt strength and even wall thickness.
- Film (carrier bags, liners): controlled MFI and density for bubble stability and strength.
- Pipe (PE80 / PE100): pressure-rated grades with long-term hydrostatic strength.
- Injection moulding (housewares, crates): higher MFI for easy filling of complex parts.
Then match MFI and density
As a rule of thumb, a lower MFI means a higher-viscosity melt - better for blow moulding and pipe, where melt strength matters. A higher MFI flows more easily and suits injection moulding. Density influences stiffness and barrier: higher density gives more rigidity and chemical resistance.
Don't forget the documentation
For any imported resin, insist on a certificate of analysis (COA) confirming MFI, density and grade, plus batch traceability. This is what lets you reproduce results run to run and troubleshoot quickly if something drifts.
Talk it through before you order
If you are unsure, share your application, target output and any spec from your current supplier. We will match it to a producer grade and return a landed-cost quote. See our HDPE grades or contact the sourcing desk.