Table of Contents
Reviewed and updated by ICD - Week 37/2026
Melt Flow Index (MFI) - also called Melt Flow Rate (MFR) - is a key specification for HDPE plastic that determines how the material flows during processing and directly affects the mechanical properties of finished products.
What is Melt Flow Index?
Melt Flow Index (MFI), standardized as Melt Flow Rate (MFR) per ISO 1133 and ASTM D1238, measures how easily a thermoplastic melt flows under a standard set of conditions. For HDPE, the test measures the mass of polymer (in grams) that flows through a standard capillary die in 10 minutes at 190 degrees C under a 2.16 kg load (HDPE standard condition).
The result is expressed in g/10 min. A low MFI indicates a high-viscosity (thick) melt; a high MFI indicates a low-viscosity (thin) melt.
MFI and molecular weight relationship
MFI is inversely related to molecular weight:
- Low MFI (0.1-1 g/10min) = high molecular weight = long polymer chains = more entanglement = better mechanical properties (toughness, impact resistance, ESCR) but harder to process
- High MFI (5-20 g/10min) = low molecular weight = shorter chains = easier to flow = faster processing but lower mechanical performance
HDPE MFI ranges and applications
| MFI range (g/10min) | HDPE type | Processing method | Typical applications |
|---|---|---|---|
| 0.1 - 0.5 | HMWPE / UHMWPE | Compression moulding, ram extrusion | Pipes, liners, wear plates |
| 0.5 - 1.5 | High MW HDPE | Blow moulding, extrusion | Large containers, fuel tanks, drums |
| 1.5 - 5 | Standard HDPE | Injection moulding, extrusion | Crates, pallets, pipe fittings |
| 5 - 15 | Low MW HDPE | Injection moulding (fast cycle) | Thin-wall packaging, caps, closures |
| 15+ | Specialty grades | Rotomoulding, specialty injection | Large hollow containers |
Why MFI matters for HDPE pallet manufacturing
For injection-moulded HDPE plastic pallets, MFI selection is a critical engineering decision. ICD Vietnam’s HDPE pallets use grades typically in the 2-5 g/10min range - this balances:
- Processability: Flows well enough to fill large, complex pallet moulds completely without short-shots or weld line defects
- Mechanical performance: Sufficient molecular weight for good impact resistance, fatigue strength under repeated forklift loading, and ESCR (environmental stress crack resistance)
- Dimensional stability: Low shrinkage and warpage after demoulding - critical for flat pallet surfaces
MFI test conditions for HDPE
| Standard | Test temperature | Load | Designation |
|---|---|---|---|
| ISO 1133 / ASTM D1238 | 190 degrees C | 2.16 kg | Condition D (most common for HDPE) |
| ISO 1133 / ASTM D1238 | 190 degrees C | 5 kg | Condition E (high MW grades) |
| ISO 1133 / ASTM D1238 | 190 degrees C | 21.6 kg | HLMI - for very high MW grades |
Note: Always specify test conditions when comparing MFI values - same polymer can show very different MFI numbers under different loads.
How to interpret an HDPE datasheet MFI
- MFI reported as “0.3 g/10min (190 degrees C / 2.16 kg)” - standard injection grade, suitable for thick-wall parts
- MFI reported as “8 g/10min (190 degrees C / 2.16 kg)” - easy-flow injection grade, suitable for thin-wall or high-speed moulding
- If only HLMI (21.6 kg load) is reported, the polymer is very high MW - convert using HLMI/MFI ratio (typically 10-40x for HDPE)
Frequently Asked Questions
1. What is a good MFI for HDPE plastic pallets?
For injection-moulded HDPE pallets, grades with MFI of 2-5 g/10min (190 degrees C / 2.16 kg) are typical. This range provides good mould-fill for large pallet cavities while maintaining adequate impact resistance and ESCR for industrial use.
2. Does higher MFI mean better quality HDPE?
No - higher MFI means easier processability but generally lower mechanical properties (impact resistance, stress crack resistance). For structural applications like pallets and crates, lower MFI grades with higher molecular weight are preferred. Higher MFI is appropriate for thin-wall packaging requiring fast cycle times.
3. What is the difference between MFI and MFR?
Melt Flow Index (MFI) and Melt Flow Rate (MFR) are the same measurement. MFR is the current ISO 1133 terminology; MFI is the older ASTM D1238 term. Both measure mass flow (g/10 min) under standardized temperature and load conditions.
Contact ICD Vietnam - HDPE and PP plastic pallets
Hotline 24/7: 0983 797 186 | 090 345 9186 | 090 5859 186
Zalo: icdvietnam | Email: sales@icdvietnam.com.vn
References
- ISO 1133-1:2022 - Plastics - Determination of melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics
- ASTM D1238 - Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer
- Wikipedia: Melt flow index
Typical HDPE MFI values by processing method
Each HDPE conversion process needs a specific MFI window. Grades that flow well for thin-wall injection moulding are too soft for pipe extrusion, while pipe-grade resins will not fill a thin packaging mould. The table below maps common HDPE applications to their working MFI range and explains how viscosity drives the result.
| Process / application | Typical MFI (g/10min) | Why this range |
|---|---|---|
| Pipe extrusion | 0.1 - 0.5 | Very high viscosity holds wall shape and gives best ESCR for pressure pipe |
| Blow moulding (bottles, drums) | 0.3 - 1.0 | Stiff melt supports the parison without sagging during inflation |
| Injection moulding (pallets, crates) | 2 - 5 | Fills large cavities fully while keeping impact strength and stiffness |
| Blown film | 0.5 - 2.0 | Moderate viscosity keeps a stable bubble and good tear strength |
| Thin-wall injection (caps, closures) | 5 - 15 | Low viscosity allows fast cycles and complete thin-section fill |
The pattern is consistent: a low MFI means high melt viscosity, longer polymer chains and stronger parts that are harder to push through a die, while a high MFI means a thin melt that flows fast but trades away impact resistance and stress crack resistance. For load-bearing items such as HDPE plastic pallets, ICD Vietnam selects 2 - 5 g/10min grades to keep both mould-fill and durability in balance. Need help matching an HDPE grade to your application? Call ICD Vietnam on 0983 797 186.
Reference
Melt Flow Index (MFI) testing for HDPE plastic - Society of Plastics Engineers (SPE).
