MFR/MVR: Common Terms

Over the years, quite a number of different terms have become established in the field of melt flow measurements, often with the same or similar meanings. This sometimes leads to misunderstandings and the whole subject area seems more complicated than it actually is.

Even for the test instruments themselves, different terms are in use, all of which describe the same test instrument:

  • Melt Index Tester
  • Melt indexer
  • Melt flow index tester
  • Melt-Flow Indexer
  • Capillary rheometer (special design)
  • Extrusion Plastometer (designation according to ASTM D1238 and ISO 1133)
  • MFR Tester
  • MVR Tester
  • MI Tester
  • MFI Tester

The reason for this variety of terms is also the different designations for the indexes themselves. The melt mass-flow rate in g/10 min - abbreviated MFR - according to ISO 1133 is sometimes abbreviated and named differently:

  • Melt Flow Rate: MFR (designation according to ASTM D1238)
  • Melt Flow Index: MFI
  • Melt index: MI

The melt volume-flow rate - MVR for short - in cm³/10 min according to ISO 1133 is also sometimes referred to differently:

  • Melt Volume Rate: MVR (designation according to ASTM D1238:2013)
  • Melt Volume Index: MVI

In ISO 1133 and ASTM D1238, the flow rate ratio, or FRR for short, was previously sometimes referred to as the melt flow ratio and confusingly abbreviated as MFR.

The individual components of the plastometers are also sometimes referred to differently:

In ISO 1133 and ASTM D1238, the test barrel is referred to as a "cylinder". The extrusion tool is called “die” by the standards and is also sometimes called “capillary”.


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