Home / Wood Compare / Thermally Modified Oak vs ThermoWood Ash Thermo-D
Professional Comparison · Source-attributed engineering data · Updated 19 July 2026
Thermally Modified Oak VS ThermoWood Ash Thermo-D
Which wood is better for your project? Scores are computed from the verified figures on each species page — how we score.
🥇
Thermally Modified Oak
61/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Higher durability (EN 350 Class 1 vs Class 2)
🥈
ThermoWood Ash Thermo-D
56/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Harder wear surface
- Solid choice where its profile fits the project
Visual comparison
Thermally Modified OakThermoWood Ash Thermo-D
Winner by category
There isn't one universally best wood — there's a best wood for each purpose.
| Category | Winner |
|---|---|
| Durability | Thermally Modified Oak |
| Stability | Tie |
| Hardness | ThermoWood Ash Thermo-D |
| Strength (MOR) | ThermoWood Ash Thermo-D |
| Stiffness (MOE) | ThermoWood Ash Thermo-D |
| Flame spread | Tie |
| Machining ease | Thermally Modified Oak |
| Lightness | ThermoWood Ash Thermo-D |
Engineering data
| Property | Thermally Modified Oak | ThermoWood Ash Thermo-D |
|---|---|---|
| Janka Hardness | 1120UNV lbf | 1320UNV lbf |
| Density | 0.68ITWA g/cm³ | 0.55ITWA g/cm³ |
| MOE | 11.0ITWA GPa | 13.3ITWA GPa |
| MOR | 78.0ITWA MPa | 90.0ITWA MPa |
| Durability | Class 1 Very Durable (treated) | Class 2 Durable (treated) |
| Stability | Good | Good |
| Fire (E84) | Not classified | Not classified |
| Radial Shrink | 1.8ITWA % | 1.7ITWA % |
| Tangential Shrink | 3.5ITWA % | 3.2ITWA % |
| T/R Ratio | 1.94 | 1.88 |
Figures carry the same source status as the species pages they come from — verified where cited, indicative where marked.
Best for
| Application | Recommended | Suitability |
|---|---|---|
| Outdoor decking / pergola | 🥇 Thermally Modified Oak | ★★★★☆ |
| Exterior cladding | 🥇 Thermally Modified Oak | ★★★★☆ |
| Flooring / wear surfaces | 🥇 ThermoWood Ash Thermo-D | ★★★☆☆ |
| Furniture / interior joinery | 🥇 Thermally Modified Oak | ★★★☆☆ |
| Structural / load-bearing | 🥇 ThermoWood Ash Thermo-D | ★★☆☆☆ |
| Sauna / wet interiors | 🥇 Thermally Modified Oak | ★★★★☆ |
Advantages & limitations
Thermally Modified Oak
Advantages relative to ThermoWood Ash Thermo-D
Limitations relative to ThermoWood Ash Thermo-D
- Janka is 1,120 lbf vs 1,320 lbf, about 15% lower
- MOR is 78 MPa vs 90.6 MPa, about 14% lower
- MOE is 11.0 GPa vs 13.3 GPa, about 17% lower
ThermoWood Ash Thermo-D
Advantages relative to Thermally Modified Oak
- Janka is 1,320 lbf vs 1,120 lbf, about 18% harder
- MOR is 90.6 MPa vs 78 MPa, about 16% higher
- MOE is 13.3 GPa vs 11.0 GPa, about 21% higher
Limitations relative to Thermally Modified Oak
Recommendation
Choose Thermally Modified Oak if…
- Exterior cladding, decking, interior flooring and panelling where the modified oak profile matches the specification and the working properties are sufficient
- Joinery and feature surfaces where the oak grain and appearance are the aesthetic preference
Choose ThermoWood Ash Thermo-D if…
- Decking (a signature application), exterior cladding and interior flooring where the higher hardness and bending strength are what the piece must deliver
- Garden furniture and joinery where dent resistance in service matters
Frequently asked questions
Which is more durable, Thermally Modified Oak or ThermoWood Ash Thermo-D?
Thermally Modified Oak — it carries the better EN 350 rating (Class 1 vs Class 2). Lower class numbers mean higher natural durability.
Which wood is better for outdoor use?
Thermally Modified Oak — outdoor performance combines decay durability with dimensional stability, and it leads on that combination.
Is Thermally Modified Oak harder than ThermoWood Ash Thermo-D?
No — ThermoWood Ash Thermo-D is harder (Janka 1320 vs 1120 lbf).
How we score. Each Library Score is a weighted composite of the verified figures above, expressed as a percentile against our 60-species library. Cost is handled qualitatively, never scored. Full weighting and what it excludes.