Key takeaways
- Sample preparation matters more than the number. Moulded and printed samples are not comparable.
- Tensile strength tells you when it breaks; elongation tells you whether it warns you.
- HDT is measured under a stated load. Quoting it without the load is meaningless.
- A sheet with no test standard, no orientation and no tolerance is marketing, not data.
Two spools can carry the same headline number and behave completely differently on your printer. That is not always dishonesty — it is usually that the two sheets measured different things. Reading them in the right order makes the differences visible.
Start at the bottom of the sheet
The footnotes decide how to interpret everything above them. Three lines matter most.
- Test standard. ISO 527 and ASTM D638 both measure tensile properties, on different specimen shapes at different rates. Numbers from the two are close, not interchangeable.
- Sample preparation. Injection moulded, or 3D printed? This is the largest single source of difference on any filament data sheet.
- Conditioning. Was the sample dried before testing, and at what humidity was it tested? For nylon, this alone moves tensile strength by a third.
What each number is actually telling you
Tensile strength (MPa)
The stress at which the sample fails in tension. Useful for ranking materials, and almost never the number that decides a real part — because real parts fail in bending, at stress concentrations, or across a layer boundary.
Elongation at break (%)
How far it stretches before failing. This is the most under-read number on any data sheet. 4 % means brittle: it will snap with no deformation. 180 % means it will bend, then keep working. Two materials with identical tensile strength and very different elongation are not substitutes for each other.
Flexural modulus (MPa)
Stiffness in bending — how much the part deflects under load. If your complaint about a part is that it flexes rather than that it breaks, this is the number to compare, and fibre-filled grades are where it climbs.
Heat deflection temperature (°C)
The temperature at which a loaded bar deflects by a set amount. It is always measured under a specified load — commonly 0.45 MPa or 1.8 MPa — and the two figures for the same material can be 20 °C apart. A sheet quoting HDT with no load is quoting nothing.
Izod or Charpy impact (kJ/m²)
Energy absorbed in a sudden break, notched or unnotched. This is the number that predicts whether a dropped part survives, and it is where PLA looks worst and polycarbonate looks extraordinary.
Glass transition and melting point
Glass transition is where the polymer softens; it sets your drying temperature and your realistic service temperature. Melting point matters for processing, not for use. For amorphous polymers like ABS and PC there is no true melting point, and a sheet listing one is copying from somewhere else.
The process numbers that matter more
Mechanical properties get the attention; these decide whether the print succeeds.
| Number | Why it matters | What good looks like |
|---|---|---|
| Diameter tolerance | Drives extrusion consistency and surface finish | ± 0.02 mm or better for 1.75 mm |
| Roundness / ovality | An oval filament under-extrudes on one axis | Stated, not omitted |
| Moisture content as shipped | Tells you whether you must dry before first use | Stated, with sealed packaging |
| Density (g/cm³) | Converts spool weight into printable length and part mass | Always present |
| Recommended nozzle range | A range, not a single number, shows it was tested | 20–30 °C wide |
| Batch or lot number | Lets you trace a bad print to a specific batch | Printed on the spool |
Five questions a good sheet answers
- Were these values measured on printed samples, and in which orientation?
- What layer height, nozzle temperature and wall count produced them?
- What load was the HDT measured under?
- What is the diameter tolerance, and is ovality controlled?
- Which batch does this sheet describe?
If a sheet cannot tell you how the sample was printed, it is not describing anything you can print.
How we publish ours
Every ZORVA grade ships with a Material Passport that carries the print settings we validated, the batch, and the drying schedule — on the spool and on the product page, before you buy. The numbers on this site are stated per family rather than per colour, because a pigment change should never quietly change a data sheet.
Compare any two grades side by side from the materials index, or start from the job the part has to do in the material finder.
Frequently asked
Why is my printed part weaker than the data sheet says?
Most published filament values are measured on injection-moulded samples, which are solid and isotropic. A printed part is welded beads with microvoids between them, typically 30–50 % weaker across layers. Print orientation, wall count and interlayer temperature explain most of the remaining gap.
What does heat deflection temperature mean for filament?
It is the temperature at which a loaded test bar deflects by a defined amount, measured under a stated load — usually 0.45 MPa or 1.8 MPa. The two figures for one material can differ by around 20 °C, so an HDT quoted without its load is not usable for comparison.
Is tensile strength the best measure of a strong filament?
No. It tells you the stress at failure in one direction, but most real parts fail in bending, at a stress concentration, or across a layer boundary. Elongation at break and impact energy usually predict real-world survival better.
What diameter tolerance should I look for in filament?
± 0.02 mm on 1.75 mm filament is a reasonable expectation for engineering-grade material, and ± 0.03 mm is normal for fibre-filled grades. Roundness matters as much as diameter: an oval filament under-extrudes on one axis regardless of its average measurement.