There is a version of yellowing resistance in the quotation and a different one in the goods. The gap between them is a tolerance, and it is where the money is.
What yellowing resistance actually controls in PVC slats
The test that separates outdoor-grade from indoor-grade PVC.
The consequence is that this figure sets the floor for everything downstream: the process, the price and the failure mode all follow from it.
For PVC blinds and slats, the working range is QUV 300-500 h, dE <= 3. Inside that band the choice is commercial; outside it, the product changes category and so does the price.
What QUV 300-500 h, dE <= 3 does not tell you
| Position | Value | Effect on PVC slats | Where it shows up |
|---|---|---|---|
| Floor | QUV 300 | Lowest cost, least margin for process variation | Woodgrain film peeling within a season |
| Working middle | QUV 300-500 h, dE <= 3 | Predictable performance at a normal price | Nothing to negotiate, nothing to explain |
| Ceiling | 500 h, dE <= 3 | Best performance, highest cost | Cost the end product may not recover |
The middle is where most programmes should sit, and it is the hardest position to defend in a price meeting because it has no story attached to it.
The figure that decides the outcome is not yellowing resistance itself but the tolerance around it. A supplier who quotes QUV 300-500 h, dE <= 3 without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.
How to measure yellowing resistance
The reference method here is Colour fastness to light, run to ISO 105-B02, with an acceptance of >= grade 4. The method is the easy part; sampling and conditioning are where reports diverge.
Condition the sample before measuring. Results in this family move by 10-20 % between a dry laboratory and a humid one, and two labs can disagree on the same material without either being wrong.
Record the measured value rather than pass or fail. A marginal pass on yellowing resistance tells you the process is running at the edge, which is the information you need before the next lot rather than after it.
Yellowing resistance does not stand alone
Yellowing resistance moves with heat deflection (>= 65 C) and with colour (white / woodgrain / solid colours). Tightening one usually costs money in another, and a supplier who accepts every tolerance without comment has either not understood the interaction or is planning to substitute.
If a quotation is significantly cheaper, the difference is usually in one of these neighbours rather than in the figure being discussed.
The clause to write for yellowing resistance
The line below is the version we can quote against without inventing anything. Yellowing resistance appears with a tolerance and a test, not as a standalone number.
PVC venetian blind, 50 mm slat, 2.0 mm wall, UV stabilised, QUV 300 h dE <= 3, HDT >= 65 C, co-extruded woodgrain, cordless to EN 13120
Write it once and reuse it. The buyers who avoid claims are not stricter than everyone else; they send the same well-written clause every time.
When yellowing resistance goes wrong
Woodgrain film peeling. The decorative film lifts at the edges.
The cause is usually laminated film without adequate primer or edge sealing.
The test that catches it: Cross-hatch plus 72 h at 40 C / 90 % RH.
What to specify instead: Co-extruded woodgrain for contract work; laminated film only for dry indoor use.
None of this is visible in a quotation. It becomes visible in a retained sample and a lot record, which is why the paperwork matters more than the price on this parameter.
Four questions about yellowing resistance, before you order
- What tolerance do you hold on yellowing resistance, and what did your last three lots measure against it?
- Which method do you use for colour fastness to light, and which laboratory signs the report?
- When yellowing resistance falls outside QUV 300-500 h, dE <= 3, do you rework, downgrade, or ship and hope?
- Which of heat deflection or colour would you move first to hit a lower price?
The answers are more useful than a certificate, because they show whether the process is controlled or merely inspected. Full ranges for PVC slats are on the product page, and the measurement regime is described on the quality control page.
Questions buyers ask before ordering
Can you supply fire-rated PVC?
Yes to EN 13501 B-s1,d0 with certification, at a price premium and a longer lead time.
Will white PVC yellow in a sunny window?
Not if it is properly stabilised. Ask for a QUV 300 h report with dE <= 3. Without that report, assume it will yellow.
Questions worth asking before the price is agreed
The questions below are the ones that cannot be answered from a catalogue, which is exactly why they are worth asking.
| Question | Answer that should worry you | Answer that holds up |
|---|---|---|
| Who signs the test report, and against which standard? | “Our QC department signs it.” | A named standard, a named method and a signature that belongs to somebody who can be asked again next year. |
| How do you hold thickness inside 1.8-2.5 mm? | “That is standard for us, no problem.” | The last three lots’ readings, the instrument used and who signs the report. Heat warping starts here. |
| What happens if yellowing resistance misses the QUV 300-500 h, dE <= 3 requirement? | “It will not happen.” | A re-test clause, the tolerance on the re-test, and the point at which the lot is remade rather than discounted. |
Failure modes worth a clause in the purchase order
Claims rarely come from a batch that was obviously wrong. They come from a uv stabiliser figure that sat inside the quoted band and outside what the product needed.
| Failure | What triggers it | Test to demand on the production lot |
|---|---|---|
| Heat warping | Heat deflection temperature below the in-window temperature. | Yellowing — QUV 300 h; acceptance dE <= 3 |
| Cold brittleness | High filler content (calcium carbonate) to cut cost. | Heat deflection — ISO 75 / 60 C load test; acceptance no visible warp |
The other two, with acceptance numbers attached, are in the full failure analysis for PVC slats. A supplier who cannot name the mode he sees most often is describing a catalogue, not a process.
Need yellowing resistance specified and tested against your end use?
Send a window schedule or a single set size and we will return a quotation with the loading plan, the safety standard that applies to your market and the lead time for the colour you need. Catalogue and current price list on request.
Related reading
Catalogue and current price list · Neutral packing and private label · Consolidation, documents and lead times
