What the Filament Properties on SpoolScout Mean (MFI, Bending Modulus, Impact Strength)

Updated

SpoolScout lists a set of material properties for each filament — MFI, bending modulus, bending strength, impact strength, density, and a print temperature range. These are datasheet values that describe how the plastic behaves, not how a specific print will turn out. Use them to narrow candidates and sanity-check a purchase; use the print temperature range as a starting point for your slicer, then tune from there. The numbers are most useful when compared between filaments of the same type (PLA vs. PLA, PETG vs. PETG), because a "high" value only means something relative to the rest of that family.

The properties at a glance

Property Unit on SpoolScout What it tells you Practical use
MFI (melt flow index) g/10 min How easily the melted plastic flows Judging extrusion behavior and print speed headroom
Bending modulus MPa Stiffness — resistance to bending without deforming Parts that must hold shape under load
Bending strength MPa Stress at which the material breaks when bent Load-bearing brackets, structural parts
Impact strength kJ/m² Energy absorbed before fracture (toughness) Parts that get dropped, knocked, or flexed
Density g/cm³ Mass per volume Estimating part weight and cost per part
Print info °C Recommended nozzle temperature range Slicer starting point

MFI (melt flow index)

MFI measures how many grams of molten polymer flow through a standard die in 10 minutes under a set load and temperature. A higher number means the melt is runnier and flows more easily; a lower number means it is thicker and resists flow.

  • Higher MFI generally extrudes more readily, which can support faster printing and finer detail, but the melt is less resistant to sagging and the part may be weaker.
  • Lower MFI tends to give better layer strength and dimensional stability, but may need slower speeds or higher temperatures to extrude cleanly.

On SpoolScout you can see this directly: Overture PLA Plus lists 7.3 g/10 min, while standard Overture PLA lists 9 g/10 min. Same brand, same base chemistry, but the Plus variant flows less — consistent with it being a tougher, less brittle formulation. MFI is only comparable between materials tested under the same conditions, so treat it as a relative signal within a product line, not an absolute spec.

Bending modulus and bending strength

These two are often confused, so keep them separate:

  • Bending modulus (MPa) is stiffness. It describes how much the material deflects under a given force before it permanently bends. Higher = stiffer, more dimensionally rigid.
  • Bending strength (MPa) is the stress at which it actually fails in bending. Higher = it takes more force to break it.

A material can be stiff but brittle (high modulus, low impact strength), or flexible but tough. Using the SpoolScout data: Overture PLA Plus shows a bending modulus of 2394 MPa and bending strength of 61.4 MPa, while standard Overture PLA shows 3279 MPa and 84.9 MPa. Standard PLA is the stiffer and stronger of the two in bending — but that is exactly why PLA Plus exists: it trades some stiffness for toughness, which shows up in the impact strength column.

Impact strength

Impact strength (kJ/m²) measures how much energy the material absorbs before it fractures — in plain terms, how well it survives being dropped or hit. This is the number to check when a part will take knocks rather than steady load.

  • High impact strength = tough, resists cracking and shattering.
  • Low impact strength = brittle, can crack along layer lines under sudden force.

This is the property most often missing from the SpoolScout rows shown (many entries list a dash), so when it is present, treat it as a strong differentiator. If your part is a tool handle, a clip, or anything that gets bumped, prioritize impact strength over bending modulus.

Density

Density (g/cm³) is mass per unit volume. It matters for two practical reasons: estimating how much a printed part will weigh, and comparing cost per part rather than cost per spool. A denser filament at the same price per kilogram gives you slightly less volume of plastic, so a lighter-density material can be the better value for large prints even at an identical price/kg.

Print temperature range

The "Print info" column gives a recommended nozzle range — for example 190–230 °C for Overture PLA Plus and 190–220 °C for standard Overture PLA. This is a starting window, not a fixed setting.

  • Start in the middle of the range for a first test print.
  • Move toward the lower end for better bridging and detail; toward the upper end for stronger layer adhesion and faster flow.
  • If you change print speed significantly, re-check temperature — faster printing usually needs more heat to keep up.

How to use these numbers when choosing

  1. Filter by type first (PLA, PETG, etc.), then compare properties only within that type.
  2. Match the property to the job. Stiffness for structural brackets, impact strength for parts that get hit, MFI when you care about print speed or fine detail.
  3. Check density and price/kg together to compare real cost per part, not just per spool.
  4. Use the temperature range as your slicer starting point, then run a small test print before committing to a long one.
  5. Treat missing values as unknown, not zero — a dash in the impact strength column means the data isn't listed, so don't assume the filament is brittle.

One caveat worth keeping in mind: SpoolScout notes that it receives commissions for purchases made through links on the site, so the "Buy on Amazon" links are affiliate links. The property data itself comes from manufacturer datasheets, which describe the raw material under lab conditions — your printed part's real-world performance also depends on layer height, infill, orientation, and cooling, so use these numbers to shortlist and verify, not to predict a print exactly.