Melt Flow Index Testing for Thermoplastics

Be in the know about polymer flow.

In the thermoplastic industry, polymer resins are melted for processing and then molded or extruded. These materials then solidify as they cool and become countless products we use every day.

When you need answers about the processability of thermoplastic polymers, Industrial Inspection & Analysis (IIA) can help. Our polymer analyses provide detailed data about the chemical and physical properties of polymers. Our services include melt flow indexing, a measurement that provides valuable insight into the processability of thermoplastics.

What is Melt Flow Index Testing?

A type of materials property test, melt flow index testing measures the rate that the melted thermoplastic material flows and, thus, provides valuable insight into how easily it can be processed. Also known as melt flow rate (MFR), the melt flow index (MFI) quantifies a polymer’s flowability or melt viscosity.

Melt flow index testing is a fairly simple test. Here’s how it works:

  1. A polymer sample is heated to a specific temperature in our melt flow index tester, also known as an extrusion plastometer.
  2. A piston pushes the molten material through a capillary die.
  3. We measure the mass of the extruded polymer after a set amount of time to determine the MFI/MFR.

The MFI/MFR measurement is reported in grams of polymer per 10 minutes. Typically, the higher the MFI, the faster the flow. Along with melt flow rate, our testing can also quantify melt flow volume.

Melt Flow Index Testing Applications

Here are just a few of many applications for melt flow index testing:

  • To better understand how a plastic will react during the extrusion process
  • To quantify thermoplastic viscosity (how easily it will flow)
  • To ensure a suitable material is selected for your specific process
  • For comparative analysis to determine why a certain polymer is underperforming or to determine its molecular weight


With roots that date back more than a century, IIA has grown to become one of the largest and most trusted providers of lab services in North America. Our ISO-accredited testing lab uses the latest technologies and experienced personnel to provide timely, accurate results to customers in an array of industries. Our capabilities include metallurgical, non-destructive, dimensional, mechanical, EMC/EMI, consumer goods, calibration, environmental and chemical analysis. As a full-service provider, the entire IIA team is on tap to help resolve questions or issues related to your polymer analysis.

Learn more about IIA’s Polymer Analysis.


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