A certificate of analysis (COA) is only valuable if it is specific, measured and traceable. Most filament COAs are none of the three: they repeat the brochure specification and add a date. Here is what to demand instead.
Brochure spec vs real batch report
| Field | Brochure-style COA | Traceable batch report |
|---|---|---|
| Lot number | Missing or generic | Unique, and printed on the spool |
| Values | Copies the specification | Actual measured results for the lot |
| Limits | Absent | Stated pass/fail limits beside each result |
| Method | Absent | Test method referenced per property |
| Traceability | None | Polymer batch, machine, operator/shift, date |
| Approval | None | Named sign-off |
What to measure, and why
- Diameter and roundness — the two properties that cause clogs and inconsistent extrusion. Ask for the measured distribution, not just the mean.
- Color deviation (ΔE) — the number that decides whether a repeat order matches the first. See color consistency.
- Mechanical values — tensile, elongation and impact for engineering grades, so a batch can be compared against the TDS.
- Moisture — critical for nylon and PC, often omitted.
How traceability pays for itself
- Faster complaint resolution. A customer reports poor printing; you look up the lot and know the measured values before you reply.
- Safer reorders. Lot history shows whether a grade is stable across runs or drifts.
- Cleaner audits. Retail and industrial buyers increasingly sample-test incoming material and ask for the matching record.
- Better color control. ΔE history tells you when a masterbatch needs review before customers notice.
Questions to ask your supplier
- Does every shipment include a batch report with measured values?
- Does the lot number on the report match the spool and the packing list?
- How long are samples and records retained?
- Can you send the report for the specific lot I am about to receive?
VOXFIL codes every spool to a production lot and issues a batch report with each order covering the properties above, alongside TDS/SDS and declarations. See the Trust Center for the scope, or ask for a sample report before ordering.
Frequently asked questions
What should a filament certificate of analysis contain?
A unique lot number, the actual measured values for that lot, the pass/fail limits each value is compared against, the test method, traceability to polymer batch and production date, and a named approval.
Why does diameter distribution matter more than a single tolerance figure?
Because clogs and inconsistent extrusion come from variation, not from the average. A measured distribution shows whether the process is stable across the whole run.
How long should a supplier retain batch records?
Long enough to answer a query on a product still in the market — commonly two to three years. Ask the supplier what their retention policy is and whether retained samples are kept.