What units is Melt Flow Index expressed in?

MFI is expressed in grams per 10 minutes (g/10 min). It represents the mass of polymer pushed through a standard 2.095 mm diameter die under a specified load at a controlled temperature over a 10-minute period.

What is the difference between MFI and MFR?

Melt Flow Index (MFI) and Melt Flow Rate (MFR) are used interchangeably and refer to the same measurement. The ISO 1133 standard uses "MFR" while older ASTM D1238 literature often uses "MFI". Both describe mass flow in g/10 min.

What is a typical MFI range for common polymers?

Typical ranges vary widely: HDPE for blow molding is 0.1–1 g/10 min, injection-grade polypropylene (PP) is 10–50 g/10 min, and general-purpose polystyrene (PS) is 2–20 g/10 min. Higher MFI means easier flow but usually lower molecular weight and reduced mechanical strength.

Does the applied load affect the MFI result?

Yes. A higher load forces more polymer through the die, yielding a higher MFI number. Standard loads defined in ASTM D1238 include 2.16 kg, 5 kg, and 21.6 kg. Always report the test conditions (temperature and load) alongside the MFI value for a meaningful comparison.

What is the relationship between MFI and molecular weight?

MFI has an inverse relationship with molecular weight. High-molecular-weight polymers exhibit low MFI (high viscosity, difficult flow), while low-molecular-weight grades show high MFI (low viscosity, easy flow). This makes MFI a quick proxy for molecular weight in quality control.

Melt Flow Index Calculator

Name: Melt Flow Index Calculator
Availability: InStock
Author: Nham Vu

Calculate the Melt Flow Index (MFI) of a polymer from extruded mass, time, and load to assess processability.

Test Parameters

Enter values from your plastometer test run.

Extruded Mass (g)

Mass of polymer collected from the die orifice.

Test Duration (s)

Time interval over which the extrudate was collected.

Applied Load (kg)

Standard ASTM D1238 loads: 2.16, 5, 10, 21.6 kg.

Typical MFI Reference Values

Polymer	MFI (g/10 min)	Load
HDPE (blow molding)	0.1 – 1	2.16 kg
LDPE (film grade)	2 – 7	2.16 kg
PP (injection grade)	10 – 50	2.16 kg
ABS (general purpose)	5 – 20	2.16 kg
Nylon 6 (PA6)	10 – 25	2.16 kg
Polycarbonate (PC)	5 – 25	1.2 kg

Summary

Calculate the Melt Flow Index (MFI) of a polymer from extruded mass, time, and load to assess processability.

How it works

Weigh the polymer sample extruded from the plastometer die.
Record the time interval over which the sample was collected.
Enter the extruded mass (grams), test duration (seconds), and applied load (kg).
The calculator normalizes mass to a 10-minute window: MFI = (mass / time) x 600.
Review the MFI value and the processing suitability classification.

Use cases

Quality control of incoming polymer resins before production.
Comparing flowability of different polymer grades for a new product.
Verifying conformance to ASTM D1238 or ISO 1133 specifications.
Selecting the right polymer grade for injection molding vs. extrusion.
Monitoring batch-to-batch consistency in polymer manufacturing.
Academic labs teaching polymer processing fundamentals.
R&D evaluation of new polymer blends or additives.
Troubleshooting processing issues caused by viscosity variation.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu