Ironwood (Ulin)
Scientific name: Eusideroxylon zwageri
Overview
Ironwood, commonly known as Ulin, is one of the densest and most durable tropical hardwoods in Southeast Asia. Native primarily to Indonesia, Malaysia, and Borneo, it is renowned for its extreme hardness, resistance to decay, and long service life in harsh outdoor environments.
Because of its density and durability, Ulin has historically been used in heavy structural and marine applications where long-term performance is critical.
Quick Facts
- Common Name: Ironwood (Ulin)
- Scientific Name: Eusideroxylon zwageri
- Region: Asian Hardwoods (Southeast Asia – Indonesia, Malaysia & Borneo)
- Tree Size: 100–150 ft tall, 3–5 ft trunk diameter
- Average Dried Weight: 75 lbs/ft³ (1,200 kg/m³)
- Janka Hardness: 3,660 lbf
- Color: Dark brown to nearly black
- Grain: Interlocked
- Texture: Fine to medium
Identification Characteristics
Ulin is identified by its dark brown heartwood and extreme density. The grain is generally straight but may show slight interlocking. The wood feels noticeably heavy for its size and sinks in water.
Sapwood is pale and clearly distinct from the darker heartwood.
Key identification traits include:
- Dark brown to deep chocolate heartwood
- Very high weight and density
- Fine to medium texture
- Smooth, tight surface when finished
Working Properties
Ironwood is extremely difficult to machine due to its hardness and density.
- Very hard on tools
- Requires carbide cutting edges
- Pre-drilling mandatory for fasteners
- Sands to a smooth surface
- Exceptional dimensional stability
Because of its weight and toughness, machining should be done carefully and deliberately.
Safety Note
Dust from Ironwood may cause skin or respiratory irritation in some individuals. Proper dust extraction and protective equipment are strongly recommended when cutting or sanding.
Common Uses
Ironwood is commonly used in heavy-duty and exterior applications, including:
- Marine construction
- Dock pilings
- Bridges
- Exterior decking
- Heavy structural beams
Its extreme durability makes it especially valued in environments exposed to moisture and insects.
Sustainability & Notes
Ulin has faced significant harvesting pressure in parts of Southeast Asia. Sustainable sourcing is critical, and availability may be limited depending on region and regulation.
Buyers should verify legality and documentation when acquiring this species.
Comparative Notes & Related Species
Balau – A dense Southeast Asian hardwood commonly used for heavy outdoor construction and decking due to its durability and resistance to decay.
Merbau – Another durable tropical hardwood often used in flooring and exterior applications, typically somewhat easier to machine than Ulin.
Kempas – A strong Southeast Asian hardwood used in flooring and heavy construction, generally less durable outdoors but more workable than ironwood.
Related Guides
How to Identify Exotic Hardwood by Grain Pattern
Studying grain texture and color variation helps distinguish dense tropical hardwoods used in heavy-duty construction.
Density & Hardness Explained (Janka Scale Guide)
Understanding hardness ratings helps explain the exceptional density and durability of hardwood species.
Machining Dense Tropical Hardwoods
Very dense tropical hardwoods require sharp tools and careful machining techniques to achieve clean cuts and smooth finishes.
Compare Wood Properties
See how this species ranks in density and hardness using our Wood Density & Janka Hardness Chart. You can also explore Hardest Woods, Softest Woods, and Most Dense Woods for quick comparisons.
Collector Notes
Ironwood is valued by collectors for its density and long service history in structural applications. Well-seasoned boards with uniform dark color are typically preferred.
Due to its hardness, smaller workable pieces are often favored for specialty projects.
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Wood Sample Collection
This species is part of an ongoing effort to document and preserve wood samples from around the world.
Learn more about contributing to the collection:
Resources
Authoritative botanical and forestry references used in compiling information about this species include:
• USDA Forest Service – Wood Handbook: Wood as an Engineering Material
https://www.fpl.fs.usda.gov/products/publications/
• The Wood Database – Global reference for wood identification, physical properties, and woodworking characteristics
https://www.wood-database.com/
• Royal Botanic Gardens, Kew – Plants of the World Online – Botanical taxonomy and species distribution database
https://powo.science.kew.org/
• International Union for Conservation of Nature (IUCN Red List) – Global conservation status assessments
https://www.iucnredlist.org/
• Convention on International Trade in Endangered Species (CITES) – International trade regulations for protected plant species
https://cites.org/
Additional forestry publications, academic research papers, and regional timber studies may also be referenced where available.
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Availability & Where to Buy
Exotic hardwood availability can vary significantly depending on region, sustainability regulations, and supplier inventory.
As this archive grows, recommended suppliers and specialty wood retailers will be listed here to help woodworkers locate responsibly sourced material.
Lumber Suppliers:
Availability varies — see the Where to Buy Exotic Woods page for current sources.
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