MFI vs MVR: How to Choose Plastic Resin Flow for Injection Molding and Extrusion
Understand MFI and MVR before selecting plastic resin. Learn why test conditions, flow path, melt strength and processing method matter more than one number.
What Is the Difference Between MFI and MVR?
- Test standard, such as ISO 1133 or ASTM D1238
- Test temperature
- Applied load
- Whether the value is MFR/MFI or MVR
- Exact resin family and grade
- Current-batch COA versus typical TDS value
Why Test Conditions Matter
Injection Molding: Flow Is Only One Part of the Decision
- Part thickness
- Flow-length-to-thickness ratio
- Gate position
- Mold temperature
- Required impact or stiffness
- Cosmetic appearance requirements
- Cycle-time target
Extrusion and Blow Molding: Evaluate Melt Strength Too
- Die design
- Drawdown or stretch requirement
- Thickness consistency
- Sag resistance
- Output rate
- Surface quality
- Downstream cooling conditions
Five Questions to Ask Before Approving a Resin Grade
- What exact process will be used?
- What are the test conditions behind the stated MFI or MVR value?
- Is the value from the current COA or only a typical TDS figure?
- What flow behavior does the existing approved grade have?
- Can the supplier provide a sample for a real production trial?