Two documents do most of the work in verifying a polymer before you buy it: the technical datasheet (TDS) and the certificate of analysis (COA). Buyers who confuse them — or accept one when they need the other — are the ones who end up rejecting loads on arrival. This guide explains what each is and how to read it.
What is a technical datasheet (TDS)?
A TDS describes what a material was engineered to be — the producer's declared properties for that grade: density, melt flow index, K-value, mechanical and thermal properties, and typical applications. It describes the intended product, not the specific load in front of you. A TDS is necessary context, but on its own it is a claim about the grade in general, not evidence about your batch.
What is a certificate of analysis (COA)?
A COA reports the measured values for an actual batch — the real test results for the material you are being offered, against the specification. This is the stronger document, and for off-spec, regrind and recycled material it is the one that matters most, because it tells you which properties are on-spec and by how much any are off. A COA turns "trust me, it's fine" into a decision you can make against your own process requirements.
How do I read a COA?
- Check it refers to the actual batch or lot you are buying, not a generic sample.
- Compare the measured values against the specification column — look for anything outside range.
- For the properties your process depends on (MFI, K-value, density, colour), confirm they sit where you need them.
- Note the test methods and date — recent, batch-specific results carry more weight.
- Treat a COA that only restates the datasheet ranges, with no measured values, as weak evidence.
When should I insist on a COA?
Always for off-spec material, and it is strongly advisable for regrind and recycled grades. For prime material, a datasheet plus batch identification is often enough, but a COA still adds confidence. For anything below near-prime, pair the COA with a physical sample — no document fully substitutes for running the material. Our guide to polymer grades explains how each condition grade should be evidenced.
Documents on a marketplace
On Prime Polymers, sellers can attach datasheets and certificates to a listing, and a free account lets a buyer see those documents in full before making contact. Membership unlocks direct messaging to request a batch-specific COA or a sample. Prime Polymers is operated by ARC Polymers Ltd, a UK polymer trading company.
Frequently asked questions
- What is the difference between a COA and a TDS?
- A technical datasheet (TDS) describes what a grade was engineered to be — the producer's declared properties in general. A certificate of analysis (COA) reports the measured test results for a specific batch. The TDS is context; the COA is evidence about the actual material.
- Why is a COA important for off-spec polymer?
- Because off-spec material failed its specification on one or more properties, and the COA tells you which ones and by how much. Without it you are guessing whether the deviation matters for your process; with it you can make an informed decision.
- Do I need a COA for prime polymer?
- For prime material a datasheet plus batch identification is often sufficient, though a COA adds confidence. For off-spec, regrind and recycled grades a batch-specific COA is much more important, ideally with a sample.
- What makes a COA trustworthy?
- It refers to the actual batch you are buying, reports measured values (not just the generic datasheet range) against the specification, states the test methods, and is recent. A COA that only restates datasheet ranges is weak evidence.