When I first started reviewing incoming material for our finishing lines, I assumed "polycarbonate" was a specification. It isn't. It's a category—and a loose one. Three years and roughly 140 incoming lots later, I've come to believe the resin family name is the least useful line on the data sheet, and the most common reason a first delivery gets rejected at our dock.

So here's the checklist I actually run, in the order I run it. Five steps. If you specify PC or TPU and you need the spec to hold up after the first order, this is the sequence that has kept our rejection rate under control.

Step 1: Pin down the end-use environment, not the marketing category

The same word on two POs can mean completely different specs. Polycarbonate for an aviation interior component is not the same animal as polycarbonate for a smart card. In aviation, flame, smoke, and toxicity drive the qualification—FAR 25.853 governs interior materials in transport-category aircraft, and hydrolysis resistance matters because cabin humidity cycles degrade standard grades faster than people expect. On a plastic card, nobody cares about smoke density. What matters is overlay thickness, print adhesion, and yellowness index under UV exposure.

I once almost released a generic PC grade for a small aviation bracket because the mechanical numbers matched the drawing. They did. The flame data didn't, and we caught it in the drawing review, not on the bench. Embarrassing—but cheaper than the alternative.

Checkpoint: write the end-use environment into the PO itself. "PC, aviation interior, FAR 25.853 compliant, hydrolysis-resistant grade" is a spec. "PC" is a conversation starter.

Step 2: Ask for the grade code and the COA, not the polymer name

This is the step most first-time buyers skip. Suppliers will quote "polycarbonate" and ship whatever is closest to the container door. Ask for the grade code, the lot number, and the Certificate of Analysis before the PO confirms.

In early 2024 we received a batch of 40,000 card blanks where the yellowness index came in at 2.1 against our spec of under 1.5. Normal tolerance in that product family is roughly 0.3. The vendor claimed it was "within industry standard." We rejected the lot, and they redid it at their cost—but only because the COA requirement was already written into the contract. Now every PO we issue includes a clause for grade-code traceability and a change-notification window.

Checkpoint: if the COA doesn't name the grade code, it isn't a COA. It's a brochure.

Step 3: Run the TPU vs silicone comparison at the conditions your users actually hit

The cutting-board question is the one that comes up most often, and it's a good proxy for every TPU-vs-silicone decision. On paper both are "food-safe, flexible, heat-resistant." In practice they fail differently.

Silicone handles sustained heat better—typical silicone boards are rated to 230°C or more, which matters if someone leaves one near a hob. TPU is tougher and more cut-resistant; the blade marks tend to self-close rather than accumulate. Both can meet FDA 21 CFR 177.2600 for repeated food contact, but the certification is not the same as the test condition. Ask which temperature and which food simulant the compliance data covers.

Checkpoint: test both materials under the dishwasher cycle and the hot-oil contact your end user will actually subject them to. Most "food-safe" failures we see are temperature-cycle failures, not formulation failures.

Step 4: For TPU yarn, validate shrinkage and dye uptake before the pilot run

TPU yarn is a discipline of its own. The properties that get advertised—elongation, tensile, abrasion resistance—are the easy ones. The ones that kill a production run are thermal shrinkage and batch-to-batch color consistency, especially if the yarn is going into a textile that will be dyed or heat-set downstream.

Ask for shrinkage data at the heat-set temperature your process will actually use. Ask for a dyed swatch from the specific lot, not the masterbatch. If the supplier can't provide either, put the run on hold. A 2% shrinkage surprise on a 500-meter run is roughly 10 meters of scrap—not ideal, workable. The same surprise on a 5,000-meter order is a different conversation.

Step 5: Treat market-share claims as claims—and the supplier shortlist as a decision you make yourself

This is the step almost everyone undersells. When you're evaluating polycarbonate or TPU providers, you'll hear the same names: Covestro, Teijin, SABIC, a few others. Public market analyses routinely place them in the leading tier, and that's fine as background. It is not a specification, and it should not be the reason you pick a supplier.

What actually matters is whether the supplier will sign a change-notification agreement, whether their lot traceability holds up after a claim, and whether the technical contact answers a data question in 48 hours or two weeks. I've had excellent deliveries from smaller producers and headaches from the biggest brand in the room. The market-share ranking didn't predict either.

Checkpoint: score every candidate on traceability, change notification, and technical response time. The brand printed on the bag is the last item on the list, not the first.

What I'd flag before you hit "approve"

A few things that still catch people:

  • Don't let "recyclable" or "sustainable" stand in for a spec. The FTC Green Guides require environmental claims to be substantiated, and a marketing word on a bag isn't substantiation. Bio-based and recycled TPU grades are real products—ask for the specific recycled content percentage and the traceability to back it up.
  • Don't accept a verbal color tolerance. If the card or cap needs to match a brand color, Delta E under 2 is the industry reference for brand-critical colors. Put the number in the spec.
  • Don't review only the last page of the COA. The failure mode is in the second page, in the property nobody checked because it wasn't on the drawing.

Five steps, one principle: the specification is what you wrote down, not what the supplier told you. Get that part right, and the rest of the audit gets shorter every quarter.