PVC blinds and slats Specification: What Each Number Actually Changes

Buyers lose money on pvc blinds and slats in a predictable way: they specify one figure tightly and leave the rest to the supplier. This is a walk through every figure that changes the outcome, in the order it matters.

Why the headline number is the least useful one

Every quotation leads with slat width. It is easy to compare and it is the number the factory can hit most cheaply. But it tells you almost nothing on its own: slat width sets the frame, and the parameters below set whether the product survives its first year in service. A buyer who compares only the headline figure is buying a sample, not a supply agreement.

For PVC slats, the practical rule is to fix the headline figure at the level your product needs and then spend your negotiating attention on uv stabiliser and yellowing resistance. Those two are where cheap goods differ from adequate goods, and they are usually absent from the quotation sheet.

The numbers that decide performance

Read the table as a set of trade-offs rather than a checklist. Moving any single line usually costs money somewhere else, and the cheapest way to hit one figure is often to let another slip.

Slat width

Typical range: 25 / 35 / 50 mm. 50 mm dominates; 25 mm is for small windows and bathrooms.

Thickness

Typical range: 1.8-2.5 mm. Hollow profiles need wall thickness specified separately from overall thickness.

UV stabiliser

Typical range: required, stated in phr. Without it, white goes yellow and colours fade within a season outdoors.

Yellowing resistance

Typical range: QUV 300-500 h, dE <= 3. The test that separates outdoor-grade from indoor-grade PVC.

Heat deflection

Typical range: >= 65 C. Slats in a sun-facing window reach 60 C+ behind glass.

How to write a PVC slats specification that protects you

A specification is only useful if a substitution becomes visible. That means writing the construction and the performance together, and naming the test that proves each one. For PVC slats, the clause has to pin uv stabiliser and yellowing resistance, because those two separate a compliant lot from an adequate one:

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

Note what is missing from that line: adjectives. No ‘high quality’, no ‘premium’, no ‘export grade’. Every clause is either a number with a tolerance or a named test. If a supplier cannot quote against a line written this way, that is information about the supplier.

Where the specification usually breaks down

The first failure is yellowing. White slats turn cream within a year in a sunny window. The cause is usually insufficient or wrong uv stabiliser; often tio2 grade rather than a true uv package. The test that exposes it before you order: QUV 300 h, measure dE and yellowing index.

The second is heat warping. Slats bow in a south-facing window in summer. It comes from heat deflection temperature below the in-window temperature. Test with Deflection test at 60 C for 4 h under load. and write the result into the purchase order, not just the enquiry.

Both failures share a pattern: they appear months after delivery, they are hard to attribute, and the cost lands on the buyer rather than the mill. That is exactly why the test belongs in the specification and the report belongs in the shipment file.

What to put in a PVC slats enquiry

1. End use and the conditions, which together decide where uv stabiliser has to sit inside required, stated in phr.
2. The one figure that must hold, with yellowing named as the proof.
3. Quantity per colour and per delivery, against a typical MOQ of 500-800 sets per colour.
4. Destination market, because compliance changes the construction, not just the paperwork.
5. A physical standard viewed under a stated light source, not a screen proof.

With those five points we can quote against a real requirement instead of a generic range. Full ranges sit on the PVC slats page, and the manufacturing side of the same question is on our quality control page.

Questions buyers ask before ordering

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.

Is PVC allowed in the EU?

Yes for window coverings, but the compound must comply with REACH and heavy-metal limits, and some buyers restrict PVC on brand policy grounds. We supply both and will tell you which is more common in your market.

How does PVC compare with basswood on price?

Typically 20-30 % cheaper per set at the same size, and lighter to ship than wood but heavier than paulownia.

Failure modes worth a clause in the purchase order

Claims rarely come from a batch that was obviously wrong. They come from a heat deflection figure that sat inside the quoted band and outside what the product needed.

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.

Seven lines that turn a quotation into a specification

Most post-delivery arguments are not about quality. They are about a document that never said which figure would be measured, on which instrument, at whose cost.

1. Colour: agree the test method with the number. Two labs, two methods, two answers, one argument.
2. Fire performance (available to EN 13501 B-s1): state where in the band this order sits. The middle of the band is not what a tolerance is for.
3. Warp tolerance: the figure you will accept inside the <= 1.0 mm per 1 m at 60 C band, the tolerance on it, and the method used to measure it.
4. Slat width (25 / 35 / 50 mm): name the number, not the word. If the answer only repeats the band, ask which point inside it is being offered for this order.
5. Deviation rule: anything outside the agreed bands is reported before shipment, not after arrival.
6. Packing and marking: shipping mark, roll or carton count and the tolerance on quantity, since a short shipment is a claim too.
7. Who inspects: third-party, in-house or none, decided in advance, with the AQL level written down.

Related reading

• Pvc Slats vs Basswood
• Yellowing resistance in PVC blinds and slats
• Bathrooms and wet rooms