Are MFR and MVR the same value?
No. MFR is mass-based and MVR is volume-based. The relationship depends on melt density under the test conditions.
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MFR vs MVR in Plastic Resin TDS: What Buyers Need to Compare
MFR and MVR are related but distinct melt-flow measurements for thermoplastics. A valid comparison must include the test standard, temperature and load, as well as the exact grade and specimen condition. These measurements are useful for material characterization and quality control, but they do not directly reproduce every processing condition on a production machine.
1. Understand the measurement terms
MFR expresses the mass of polymer flowing through a specified die over a defined time under specified test conditions. MVR expresses the corresponding volume flow under specified conditions. The values are not interchangeable without the relevant density relationship and test information.
ISO 1133-1:2022 specifies procedures for determining MFR and MVR of thermoplastics under specified temperature and load conditions.
2. Record temperature and load
A reported melt-flow value is incomplete without the test temperature and load. Two datasheets may show different numbers because the materials were tested under different conditions.
When comparing grades, first check whether the same standard, temperature, load and method were used. If not, do not treat the numbers as directly comparable.
3. Do not use MFR or MVR as the only selection criterion
Melt-flow measurements are useful for screening and quality control, but they do not capture every factor in mould filling, extrusion stability, part performance or the actual production process.
Review the complete grade TDS, application requirements, processing guidance and other relevant properties. For critical applications, use supplier support and controlled production trials.
4. Ask for the exact grade document
Confirm the manufacturer, full grade code, document revision and test method. If purchasing a specific batch, request the relevant COA where available and check whether its reported test basis matches the TDS.
If a supplier quotes an alternative grade, ask for its current TDS and compare all relevant values under equivalent conditions.
Buyer checklist
- Exact manufacturer and grade code
- MFR or MVR designation and units
- Test standard and procedure
- Test temperature and load
- Document revision and sample condition
- Other application-critical TDS properties
- Batch COA for the actual material where available
Frequently asked questions
Can MFR values be compared if the test load is different?
They should not be treated as directly comparable unless the test conditions and an appropriate comparison basis are established.
Does a higher MFR always mean a better injection-moulding grade?
No. The suitable flow depends on the part, mould, machine, process window and other material properties.
Technical references
This article provides general procurement and material research guidance. It is not a substitute for grade-specific technical documents, testing, regulatory review or written commercial confirmation. Third-party cases are attributed to their original publishers and do not imply a STOPWOO customer or supplier relationship.
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