If PVC slats fails in a way that is hard to explain, thickness is the first place to look and the last place buyers check, because it is the figure everyone assumes is under control.
What thickness actually controls in PVC slats
Hollow profiles need wall thickness specified separately from overall thickness.
It also explains why thickness is the first line a buyer loosens and the last line a claim refers to.
For PVC blinds and slats, the working range is 1.8-2.5 mm. Inside that band the choice is commercial; outside it, the product changes category and so does the price.
What 1.8-2.5 mm does not tell you
| Position | Value | Effect on PVC slats | Where it shows up |
|---|---|---|---|
| Floor | 1.8 | Lowest cost, least margin for process variation | Heat warping within a season |
| Working middle | 1.8-2.5 mm | Predictable performance at a normal price | Nothing to negotiate, nothing to explain |
| Ceiling | 2.5 mm | Best performance, highest cost | Cost the end product may not recover |
Buyers default to the floor because it is the cheapest compliant answer. That is rational until the first claim, and then the saving is measured against a replacement shipment.
The figure that decides the outcome is not thickness itself but the tolerance around it. A supplier who quotes 1.8-2.5 mm without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.
How to measure thickness
The reference method here is Heat deflection, run to ISO 75 / 60 C load test, with an acceptance of no visible warp. 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 thickness tells you the process is running at the edge, which is the information you need before the next lot rather than after it.
Thickness does not stand alone
Thickness moves with uv stabiliser (required, stated in phr) and with yellowing resistance (QUV 300-500 h, dE <= 3). 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.
When you change thickness, re-check the two neighbours before you approve the sample. Most of the samples we re-make are caused by a change in one figure that was not followed through.
The clause to write for thickness
The line below is the version we can quote against without inventing anything. Thickness 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 thickness goes wrong
Heat warping. Slats bow in a south-facing window in summer.
The cause is usually heat deflection temperature below the in-window temperature.
The test that catches it: Deflection test at 60 C for 4 h under load.
What to specify instead: Higher HDT formulation and a minimum 2.0 mm wall.
The pattern is consistent: the failure appears months after delivery, is hard to attribute, and the cost lands on the buyer. That is the argument for measuring thickness on every lot rather than on the development sample.
Four questions about thickness, before you order
- What tolerance do you hold on thickness, and what did your last three lots measure against it?
- Which method do you use for heat deflection, and which laboratory signs the report?
- When thickness falls outside 1.8-2.5 mm, do you rework, downgrade, or ship and hope?
- Which of uv stabiliser or yellowing resistance 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
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, and the test that catches each one
A specification only earns its keep if it names the failure it prevents. These are the two that matter for the PVC slats figures on this page.
| Failure | What triggers it | Test to demand on the production lot |
|---|---|---|
| Woodgrain film peeling | Laminated film without adequate primer or edge sealing. | Colour fastness to light — ISO 105-B02; acceptance >= grade 4 |
| Yellowing | Insufficient or wrong UV stabiliser; often TiO2 grade rather than a true UV package. | Fire performance — EN 13501-1; acceptance B-s1,d0 where specified |
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.
From quotation to specification in seven lines
Leave the tolerance and the method out and every dispute is settled by whoever needs the goods more.
- Slat width (25 / 35 / 50 mm): fix the value per shipment, and state who pays for the re-test if a lot lands outside it.
- Thickness: 1.8-2.5 mm is not an answer on its own. Ask for the last three lots’ actual readings and the spread behind them.
- UV stabiliser: agree the test method with the number. Two labs, two methods, two answers, one argument.
- Yellowing resistance (QUV 300-500 h, dE <= 3): state where in the band this order sits. The middle of the band is not what a tolerance is for.
- Sample retention: one production sample per lot stays with the mill for twelve months. Claims are settled against it, not against memory.
- Test reports: name the standard as well as the test. A pass on a development sample is not a pass on a production lot.
- Deviation rule: anything outside the agreed bands is reported before shipment, not after arrival.
Need thickness 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
