Home / Wood Compare / Thermowood Oak ThermoD vs Thermowood Ash ThermoD
Professional Comparison · Verified Engineering Data · Updated 19 July 2026
Thermowood Oak ThermoD VS Thermowood Ash ThermoD
Which wood is better for your project? Scores are computed from the verified figures on each species page — how we score.
🥇
Thermowood Oak ThermoD
61/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Higher durability (EN 350 Class 1 vs Class 2)
🥈
Thermowood Ash ThermoD
56/100 Library Score
🪵Hardwood🌧Outdoor💧Moisture Stable
- Harder wear surface
- Solid choice where its profile fits the project
Visual comparison
Thermowood Oak ThermoDThermowood Ash ThermoD
Winner by category
There isn't one universally best wood — there's a best wood for each purpose.
| Category | Winner |
|---|---|
| Durability | Thermowood Oak ThermoD |
| Stability | Tie |
| Hardness | Thermowood Ash ThermoD |
| Strength (MOR) | Thermowood Ash ThermoD |
| Stiffness (MOE) | Thermowood Ash ThermoD |
| Flame spread | Tie |
| Machining ease | Thermowood Oak ThermoD |
| Lightness | Thermowood Ash ThermoD |
Engineering data
| Property | Thermowood Oak ThermoD | Thermowood Ash ThermoD |
|---|---|---|
| Janka Hardness | 1120ITWA lbf | 1320ITWA lbf |
| Density | 0.68ITWA g/cm³ | 0.66ITWA g/cm³ |
| MOE | 11.0ITWA GPa | 11.5ITWA GPa |
| MOR | 78.0ITWA MPa | 90.0ITWA MPa |
| Durability | Class 1 Very Durable (treated) | Class 2 Durable (treated) |
| Stability | Good | Good |
| Fire (E84) | Class C indicative | Class C indicative |
| 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 | 🥇 Thermowood Oak ThermoD | ★★★★☆ |
| Exterior cladding | 🥇 Thermowood Oak ThermoD | ★★★★☆ |
| Flooring / wear surfaces | 🥇 Thermowood Ash ThermoD | ★★★☆☆ |
| Furniture / interior joinery | 🥇 Thermowood Oak ThermoD | ★★★☆☆ |
| Structural / load-bearing | 🥇 Thermowood Ash ThermoD | ★★☆☆☆ |
| Sauna / wet interiors | 🥇 Thermowood Oak ThermoD | ★★★★☆ |
Advantages & limitations
Thermowood Oak ThermoD
Advantages
- Rated for exterior exposure (EN 350 Class 1)
Limitations
- Few practical drawbacks within its intended uses
Thermowood Ash ThermoD
Advantages
- Rated for exterior exposure (EN 350 Class 2)
Limitations
- Few practical drawbacks within its intended uses
Recommendation
Choose Thermowood Oak ThermoD if…
- The project lives outdoors and service life is the priority
Choose Thermowood Ash ThermoD if…
- You need the harder wear surface
- Its profile matches the application better than a single overall score
Frequently asked questions
Which is more durable, Thermowood Oak ThermoD or Thermowood Ash ThermoD?
Thermowood Oak ThermoD — 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?
Thermowood Oak ThermoD — outdoor performance combines decay durability with dimensional stability, and it leads on that combination.
Is Thermowood Oak ThermoD harder than Thermowood Ash ThermoD?
No — Thermowood Ash ThermoD is harder (Janka 1320 vs 1120 lbf).
How we score. Each wood gets a weighted composite of the verified figures shown above: durability 22%, stability 18%, hardness 12%, bending strength 12%, machining ease 12%, stiffness 8%, flame spread 8%, lightness 8%. The Library Score is that composite's percentile rank within our 60-species library — 50 means the library median, 90 means it outperforms nine of every ten species we cover. No price data is scored — cost guidance is qualitative. The score summarises the data; it does not replace judgement about your specific application.