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By Deepak Kumar · Founder, Vriksai

East Asia

Paulownia

Paulownia tomentosa

Also known as kiri, empress tree, princess tree · Botanical Paulownia tomentosa

Last updated: 15 July 2026Reviewed by: Vriksai editorial team — timber trade professionalsEditorial policy

Revision history

17 July 2026 — Data re-verified in site-wide audit (formulas, sources, durability classes)
15 July 2026 — Working properties and comparable-species data cross-checked against listed sources

🪵Hardwood💧Moisture Stable🌿Sustainable

Janka Hardness

300WD

lbf

Janka (metric)

1334calc

Hardness Class

Softcalc

Density

0.28wd

g/cm³

MOE

4.4wd

GPa

MOR

38.0WD

MPa

Durability

Class 4

Slightly Durable

Fire (E84)

Class C

indicative

Thermal k

0.087

W/m·K

Green MC

100—

Fiber Saturation

30FPL

Radial Shrink

2.4WD

Tangential Shrink

3.9WD

T/R Ratio

1.62derived

Stability

Excellentcalc

About the fire rating. Indicative only, derived from density and published data — not a certified rating. Real performance depends on product, thickness, coating and installation. What our ratings do and do not certify.

Compare this wood:⚖ vs Bamboo Structural Engineered ⚖ vs Scots Pine ⚖ vs Spruce-Pine-Fir SPF All comparisons →

About Paulownia

Paulownia (Paulownia tomentosa) is a soft timber that works easily but bruises and dents in service, with a Janka hardness of 300 lbf (1,334 N) and a density of about 0.28 g/cm³. It is native to East Asia, chiefly China.

At 2.4% radial and 3.9% tangential the T/R ratio is 1.62 — typical, and manageable in interior joinery and furniture provided the gaps are designed rather than assumed. Its fibre saturation point is near 30%. Below it movement is modest at 3.9% tangential, but the 1.62 T/R ratio means one-sided sealing will still pull a panel out of flat.

At 280 kg/m³ a cubic metre of Paulownia weighs about 280 kg air-dry — that figure, the 3.9% tangential and 2.4% radial movement and the 300 lbf hardness are the three inputs the calculators below actually consume. Select Paulownia in any of them to get species-specific results for weight, moisture, shrinkage and hardness.

Working properties

How Paulownia behaves at the bench and on the machine, drawn from East-Asian timber references and international wood-technology data.

MachiningExtraordinarily light and soft — it cuts, carves and machines with almost no effort, and takes crisp detail for its weight. The flip side is obvious: it dents and crushes easily, so sharp tools and light handling matter more than power.

FasteningHolds fixings only modestly given the low density; design joints rather than relying on fasteners.

GluingGlues easily and well.

FinishingSands to a silky surface with a pale, creamy colour; it is traditionally left largely unadorned in Japanese work.

Steam bendingNot a bending timber.

DryingDries very fast with unusually little movement — a large part of its appeal.

Durability & use classification

Paulownia is rated slightly durable (EN 350 Class 4) — an interior timber. What it offers instead is weight: at roughly 280 kg/m³ it is among the lightest commercial timbers in the world, sitting between balsa and poplar and about 30% lighter than comparable American hardwoods. Fast-growing to the point of being invasive in parts of the US, it is also used as a phytoremediation species, processing industrial contaminants through its vascular system.

Typical applications & suitability

Indoor — Chosen entirely for lightness, stability and workability. Known as kiri in Japan, it is the traditional wood of the tansu chest interior — light enough to carry, stable enough to keep drawers running true.

Documented end-uses: tansu chests and cabinet interiors, musical instrument soundboards (notably the koto in Japan, China and Korea), furniture, boxes and light joinery, surfboard and model cores, veneer and panel cores, and clogs.

Comparable species

Species closest to Paulownia by density, hardness, stiffness and bending strength, computed directly from the Vriksai species dataset rather than hand-picked.

Thermally Modified Western Red Cedar380 kg/m³ · 350 lbf Sugi Japanese Cedar380 kg/m³ · 580 lbf Kail Blue Pine450 kg/m³ · 460 lbf Spruce-Pine-Fir SPF420 kg/m³ · 510 lbf

Trade alternatives. For a similarly light interior softwood, Sugi or SPF; in Japanese cabinetry it is used alongside Hinoki and sugi, which take the harder-wearing exterior faces.

Alternatives to Paulownia

Paulownia measures 300 lbf Janka at 0.28 g/cm³, EN 350 durability Class 4, movement rated Excellent. At 0.28 g/cm³ Paulownia is chosen for weight. Substitutes are ranked to keep that advantage rather than trade it away for hardness. Read the numbers against the Janka scale and EN 350 durability classes.

Step up — harder than Paulownia

For anywhere the lightness is costing you surface durability — shelf edges, drawer fronts, table tops that get used.

Western Red Cedar350 lbf · 0.32 g/cm³ · Class 2+17% Janka · exterior-rated Thermally Modified Western Red Cedar350 lbf · 0.38 g/cm³ · Class 2+17% Janka · 0.38 g/cm³ · exterior-rated Norway Spruce380 lbf · 0.43 g/cm³ · Class 4+27% Janka · 0.43 g/cm³

Closest overall match

If Paulownia is unavailable and the specification cannot change, these are the nearest substitutes across hardness, density, movement, stiffness, bending strength and durability class together — not on any single property. Lower distance means a closer match.

Kail Blue Pinematch 2.77460 lbf · 0.45 g/cm³ · Class 4460 lbf vs 300 · 0.45 vs 0.28 g/cm³ Spruce-Pine-Fir SPFmatch 2.86510 lbf · 0.42 g/cm³ · Class 4510 lbf vs 300 · 0.42 vs 0.28 g/cm³ African Mahoganymatch 2.961,070 lbf · 0.52 g/cm³ · Class 31,070 lbf vs 300 · 0.52 vs 0.28 g/cm³ · more durable (Class 3)

More durable for exterior use

Paulownia is EN 350 Class 4, so untreated exterior service is not advisable. These reach Class 1–2 at comparable hardness.

Thermally Modified Western Red Cedar350 lbf · 0.38 g/cm³ · Class 2EN 350 Class 2 vs Class 4 · modified timber Western Red Cedar350 lbf · 0.32 g/cm³ · Class 2EN 350 Class 2 vs Class 4 ThermoWood Spruce Thermo-D380 lbf · 0.45 g/cm³ · Class 2EN 350 Class 2 vs Class 4 · modified timber

Computed from measured properties only — hardness, density, movement, stiffness, bending strength and EN 350 class. Price, availability and appearance are never inputs. Figures are representative values, not consignment absolutes: two species within a few percent are equivalent until verified on the material. Full method and the rules the engine cannot break.

Substitution is a match on durability class, movement and strength — not on colour or grain. Where two candidates are close, compare them directly before specifying.

Compare Paulownia side by side

Lightweight timbers are usually compared on stiffness and surface durability rather than hardness alone. Every pairing shows the measured figures side by side; full matrix in the comparison index.

Paulownia vs Spruce-Pine-Fir SPFSide-by-side data · 510 lbf Paulownia vs Scots PineSide-by-side data · 540 lbf Paulownia vs Bamboo Structural EngineeredSide-by-side data · 1,380 lbf

Calculators relevant to Paulownia

Weighted towards span, deflection and coverage — the checks a light timber like Paulownia actually needs. Full set in the tool index.

Timber Screw Spacing Calculator (EC5 & IS 883)Joinery Shelf Sag CalculatorJoinery Wood Sealer Coverage & Cost CalculatorCommercial Volumetric Weight Calculator for FreightCommercial Timber Waste Factor CalculatorCommercial Smalian Formula CalculatorMeasurement ThermoWood Mass Loss CalculatorThermoWood Green Lumber Weight CalculatorWood Science

Understand the figures

Thermal conductivity — k-value and insulation behaviour · ThermoWood species guide — Thermo-D/Thermo-S treatment classes · Janka hardness scale — how the lbf figure is measured · Wood density reference — oven-dry vs air-dry basis.

Further reading. What is ThermoWood? · Wood moisture content explained · How to calculate board feet.

Common questions about Paulownia

Is Paulownia strong enough for furniture or flooring?

It's a softer timber at 300 lbf (1,334 N), so it dents more easily than oak or teak and isn't the first choice for high-traffic flooring. Where it shines is lighter work — panels, mouldings, interior joinery and anywhere low weight and easy machining matter more than bruise resistance. Match it to the job and it performs nicely.

Will Paulownia hold up outdoors?

Honestly, not on its own — it's rated Slightly Durable (Class 4, EN 350), so untreated it won't last long once it's exposed to weather or damp. If you want to use it outside, it needs proper preservative treatment and a maintained finish. For interior work, though, durability isn't a concern at all and you can use it freely.

How much does Paulownia move with humidity?

It has moderate movement — radial shrinkage near 2.2%, tangential near 4% (T/R ratio about 1.82). That's typical territory: nothing alarming, but worth planning for. Dry it to the moisture content that suits your service environment, leave expansion room on wide panels, and let it settle in the space for a few days before final fixing and it behaves well.

unverified no published source for this figure · FPL USDA FPL Wood Handbook GTR-190 · WD The Wood Database (Eric Meier) · calc derived from the figures above · — no published source found

Tools that use this species

Janka Database ToolHardness for 60 species Green Weight CalculatorWeight of green timber Shrinkage PredictorDimensional movement EMC CalculatorEquilibrium moisture content Fiber Saturation CalculatorFSP by species Volume Converterm3, CFT, board feet

Sources & references

The Wood Database (Eric Meier) — compiled species data, one of the references behind the panel above. Which figure comes from which reference is not recorded field by field. Spot checks show the numbers do trace to published sources, but not all to the same one: strength values for US species follow the USDA FPL Wood Handbook exactly, while European species draw on European references instead. So a figure that disagrees with any single reference here is not necessarily wrong — different bodies measure specific gravity and shrinkage on different bases. If a number matters to your work, check it against the reference you intend to rely on.
East-Asian timber references — Paulownia tomentosa (kiri) utilisation and tansu-craft data · weight, uses, cultural role
International wood-technology data — paulownia species records · working properties, growth
EN 350 — European standard for natural durability of wood · durability class

Updated 15 Jul 2026 Values are representative; wood varies with provenance, age and grade. Confirm critical structural or fire figures against a test report for your actual product.