Density in Paulownia blinds and slats: Range, Tolerance and How to Test It

Density is the figure that gets written into a purchase order and then measured by nobody. This is what it controls, how to measure it, and what happens when it drifts.

What density actually controls in paulownia

40 % lighter than basswood, which cuts freight per set substantially.

That makes it a design decision rather than a purchasing one, which is why changing it after the product is fixed costs more than changing the material.

For Paulownia blinds and slats, the working range is 0.25-0.32 g/cm3. Inside that band the choice is commercial; outside it, the product changes category and so does the price.

What 0.25-0.32 g/cm3 does not tell you

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 density itself but the tolerance around it. A supplier who quotes 0.25-0.32 g/cm3 without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.

How to measure density

The reference method here is Moisture content, run to oven-dry / pin meter, with an acceptance of 9-11 %. The method is the easy part; sampling and conditioning are where reports diverge.

Measure on the goods as delivered, not on the greige or the pre-finished material. The figure that matters is the one in the product your customer receives.

Record the measured value rather than pass or fail. A marginal pass on density tells you the process is running at the edge, which is the information you need before the next lot rather than after it.

Density does not stand alone

Density moves with slat width (25 / 35 / 50 mm) and with slat thickness (2.5-3.2 mm). 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 density

The line below is the version we can quote against without inventing anything. Density appears with a tolerance and a test, not as a standalone number.

Paulownia venetian blind, 50 mm slat, 2.8 mm, density 0.25-0.32 g/cm3, moisture 9-11 %, sanding sealer + 3 coats, warp <= 2.0 mm/m, 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 density goes wrong

Denting. Slats show dents and marks after a season of cleaning and use.

The cause is usually low density and a soft early-wood layer.

The test that catches it: Janka hardness and a drop test with a 50 g ball from 30 cm.

What to specify instead: Use paulownia for residential and low-traffic use; specify basswood or PVC for contract.

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 density, before you order

1. What tolerance do you hold on density, and what did your last three lots measure against it?
2. Which method do you use for moisture content, and which laboratory signs the report?
3. When density falls outside 0.25-0.32 g/cm3, do you rework, downgrade, or ship and hope?
4. Which of slat width or slat thickness 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 paulownia are on the product page, and the measurement regime is described on the quality control page.

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 paulownia figures on this page.

The other two, with acceptance numbers attached, are in the full failure analysis for paulownia. 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.

1. Slat thickness: 2.5-3.2 mm is not an answer on its own. Ask for the last three lots’ actual readings and the spread behind them.
2. Moisture content: agree the test method with the number. Two labs, two methods, two answers, one argument.
3. Grain (straight, coarse pores): state where in the band this order sits. The middle of the band is not what a tolerance is for.
4. Coating: the figure you will accept inside the 3-4 coats, sanding sealer first band, the tolerance on it, and the method used to measure it.
5. Who inspects: third-party, in-house or none, decided in advance, with the AQL level written down.
6. Reference sample: the signed sample is the definition of the colour, not the photograph in the catalogue.
7. Price validity: the period during which the quoted figure holds, and what happens to it when the raw-material index moves.

Related reading

• Moisture content in Paulownia blinds and slats
• Paulownia blinds and slats Specification
• Slat thickness in Paulownia blinds and slats