ThermoWood Pine Thermo-D
Also known as thermo pine, thermally modified pine, termowood · Botanical Pinus sylvestris
Revision history
- — Data re-verified in site-wide audit (formulas, sources, durability classes)
- — Working properties and comparable-species data cross-checked against listed sources
About ThermoWood Pine Thermo-D
ThermoWood Pine Thermo-D is Nordic Scots pine (Pinus sylvestris) taken through the ThermoWood process at about 212°C. It is the original. VTT developed the process around this timber in the 1990s, and most of what is sold as ThermoWood anywhere in the world is still Scots pine. Janka hardness is 540 lbf (2,402 N) at a density of about 0.48 g/cm³, which is worth saying plainly: the heat has not made it harder. Pine was a soft timber before treatment and it is a soft timber after.
Note: this is a modified product, and the panel above is modelled rather than measured. The hardness figure is the base species, because thermal modification changes hardness very little. For movement, the shrinkage and the fibre saturation point both fall after treatment, and that is why modified timber moves less across the same change in moisture. Published strength reductions vary by source; the table above uses our library figures for this pair. Modification also lowers bending strength and toughness relative to the untreated timber. Use this panel to size and to compare species, and take structural, fire, durability or movement figures from your supplier's declaration for the product you are actually buying.
What the process did change is how it behaves in weather. Radial shrinkage of 1.2% and tangential of 2.5% are roughly a third of untreated Scots pine, the board leaves the kiln re-moisturised to 4–6% rather than the 12% you get from ordinary drying, and the fibre saturation point falls to around 14%, so there is less range for it to move across in the first place. Stability, not hardness, is what you are buying.
At 420 kg/m³ a cubic metre of ThermoWood Pine Thermo-D weighs about 420 kg air-dry — that figure, the 2.5% tangential and 1.2% radial movement and the 540 lbf hardness are the three inputs the calculators below actually consume. Select ThermoWood Pine Thermo-D in any of them to get species-specific results for weight, moisture, shrinkage and hardness.
Working properties
Two things define pine at the bench, and the process only fixes one of them. It was resinous; now it is not, permanently, and that is the change most joiners notice first. It was knotty; it still is. How the board behaves once it is out of the kiln is set by the process itself, which is described in full in our guide to how ThermoWood is made. What follows is specific to this timber, drawn from the International ThermoWood Association, VTT Technical Research Centre of Finland and published thermal-modification research.
Durability & use classification
Scots pine is one of the species in Table 1 of the ITWA ThermoWood Handbook, so genuine ThermoWood Pine exists and carries the association's mark. As a Thermo-D product it is treated at around 212°C and the ITWA classifies that as durable, Class 2, tested to EN 113. Thermo-S, treated gentler at about 190°C, reaches Class 3 and stays indoors. The durability is not natural resistance in the way teak's is: it comes from the treatment breaking down the hemicelluloses that decay fungi eat, and it applies through the whole board, so there is no sapwood to trim off. ITWA is explicit that ThermoWood is not intended for load-bearing structures, and that ThermoWood is its trademark rather than a generic word. The generic term under CEN/TS 15679 is Thermally Modified Timber. Our guide to how ThermoWood is made covers the process in full.
Because Scots pine is the default, it is also the easiest board in the range to actually source and the one your supplier will quote fastest. The trade-off is grade. Pine is knotty, treatment does not change that, and the knots get more brittle along with everything else. Grade selection matters more here than on the clearer species.
Typical applications & suitability
Indoor Outdoor — Scandinavian pine is the archetypal ThermoWood feedstock — the process was built around it. Modification takes an ordinary, non-durable softwood and gives it roughly 30 years of exterior service with no chemical preservative.
Documented end-uses: exterior cladding and rain screens, decking, saunas (a signature use — low thermal conductivity and no resin to bleed), garden structures, interior panelling, and joinery.
Comparable species
Species closest to ThermoWood Pine Thermo-D by density, hardness, stiffness and bending strength, computed directly from the Vriksai species dataset rather than hand-picked.
Trade alternatives. The untreated original is Scots Pine, which is only slightly durable but can instead be pressure-treated. Compare ThermoWood Spruce, and against Accoya — acetylated rather than heat-modified, reaching Class 1 and keeping its strength, at a considerably higher price.
What modification did to Scots Pine
ThermoWood Pine Thermo-D is not a species — it is Scots Pine after heat treatment. Both sets of figures are in our library, so the effect of the process on this timber can be stated exactly rather than described in general terms.
| Property | Scots Pine | ThermoWood Pine Thermo-D | Change |
|---|---|---|---|
| Tangential movement | 8.3% | 2.5% | -70% |
| Radial movement | 5.2% | 1.2% | -77% |
| EN 350 durability | Class 4 | Class 2 | 2 class better |
| Bending strength (MOR) | 83 MPa | 65 MPa | -22% |
| Stiffness (MOE) | 10.1 GPa | 9.5 GPa | -6% |
| Janka hardness | 540 lbf | 540 lbf | +0% |
| Density | 0.49 g/cm³ | 0.48 g/cm³ | -2% |
On this species the process buys a 70% cut in tangential movement and a 2-class gain in durability, paid for with 22% of its bending strength. A normal trade-off for this treatment class: fine for cladding and exterior joinery, size structural work off the treated figure, never the untreated one.
The mechanism — hemicellulose breakdown, why durability is through-section rather than surface-deep, and why the strength loss happens — is set out once in our guide to thermal modification and the ThermoWood species reference, rather than repeated on each treated species page. Untreated figures: Scots Pine.
Alternatives to ThermoWood Pine Thermo-D
ThermoWood Pine Thermo-D measures 540 lbf Janka at 0.48 g/cm³, EN 350 durability Class 2, movement rated Moderate. ThermoWood Pine Thermo-D is a modified timber: its durability comes from process, its strength from the base species. Substitutes are matched on both, not on the treated figure alone. Read the numbers against the Janka scale and EN 350 durability classes.
Thermal modification lowers hardness slightly, so if the treated figure is short of what the job needs, these are the harder options at comparable service durability.
Lower-hardness options at similar treated durability — usually cheaper per m³ and faster through the shop.
Modification is already doing the stability work here. These achieve equal or lower movement by species or by deeper treatment. Size the gaps with the shrinkage predictor and EMC calculator.
If ThermoWood Pine Thermo-D 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.
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.
Comparing modified timber to unmodified is a comparison of process as much as species — treatment class sets the durability, the base species sets the strength. Compare directly before substituting.
Compare ThermoWood Pine Thermo-D side by side
Modified against unmodified, and modification class against class — the comparisons that matter for treated timber. Every pairing shows the measured figures side by side; full matrix in the comparison index.
Calculators relevant to ThermoWood Pine Thermo-D
Includes the thermal-modification tools, since ThermoWood Pine Thermo-D behaves by treatment class as much as by species. Full set in the tool index.
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? · ThermoWood vs Teak · Wood moisture content explained.
Common questions about ThermoWood Pine Thermo-D
A note on the strength figures. MOR and MOE above are the ITWA ThermoWood Handbook 2025 figures for the thermally modified board, measured to EN 408 — not the untreated base species. Hardness is a different matter: ITWA publishes Brinell hardness, not Janka, and the two Brinell figures we hold (ITWA and a licensed producer) disagree under the same cited standard, so both hardness rows are marked unverified until that is resolved. ThermoWood is not available as strength-graded timber and must not be used for load-bearing structures. If you are designing to a strength value, take it from your supplier's declaration for the actual product.
Brinell hardness not shown: the two authoritative sources we hold report figures that differ by a factor of about ten under the same cited standard (EN 1534). The disagreement is under investigation and no figure is published until it is resolved.
unverified no published source for this figure · Lunawood licensed producer datasheet, named laboratory · ITWA International ThermoWood Association / VTT · calc derived from the figures above