Eusideroxylon is a genus of evergreen trees of the family Lauraceae. The genus is monotypic, and includes one accepted species, Eusideroxylon zwageri. It is known colloquially in English as Bornean ironwood, billian, or ulin.
It is native to Borneo and Sumatra, where it grows in lowland rain forests.
Eusideroxylon are hardwood trees reaching up to 50 metres in height with trunks over 2 metres (6 ft 7 in) in diameter, producing commercially valuable timber.
The wood of E. zwageri is impervious to termites, and can last up to 100 years after being cut.
The heartwood when cut is coloured light brown to almost bright yellow. During the aging process the heartwood darkens to deep reddish brown, very dark brown or almost black. The sapwood is bright yellow when cut, and darkens slightly. The wood texture is fine and even, with a straight grain or only slightly interlocked. The timber retains a pleasant lemon odour. This odour, along with the woods' natural high lustre, make it prized by cabinet-makers and fine furniture craftsmen.
Due to the excellent resistance to bacterial, fungal, insect and marine borer attack the wood is highly prized for many outdoor uses, especially as decking. Additionally, the wood's high density and easy workability lend it to particularly desirability in maritime structures, dock construction and ship building, especially Indonesia's pinisi sail-boat. Common local uses include: House construction, door construction, water butts and troughs, boat building (Pinisi), tools, tool handles, talisman, jewellery, medicinal slivers (for wounds, cuts, abrasions, bites and tooth-ache/infection), bridges, blowpipes and spear shafts.
Internationally, it is renowned for heavy construction such as a buffer between transportation trailers and heavy steel fabrications (such as boilers, pressure vessels, reactors and many others). It is also frequently found in dry docks as a timber to separate the hull of ships from the steel supporting stands. Other uses include use in boats and ships, industrial flooring, roofing (as shingles), fine indoor and outdoor furniture, coffin wood (esteemed by Chinese due to ability to withstand rot and insect attack) and tool handles (especially those exposed to continual high impact (the wood does not splinter and thus injure hands, eyes or endanger the operator on catastrophic failure) such as shovels, axes, block splitters, sledge hammers, heavy mallets, demolition hammers, mattocks, picks, hoes and hammers). Some expert cabinet-makers treasure an ulin-headed carpenter's mallet as an excellent intermediate density hammer face between the usual wood and a metal one and is able to quite easily tap or "whack" stubborn highly polished metal fixtures without damage to the face or the fixture.
Other sources indicate that ulin wood is often used for marine constructions such as pilings, wharfs, docks, sluices, dams, ships, bridges, but also used for power line poles, masts, roof shingles and house posts and to a minor extent as frame, board, heavy duty flooring, railway sleepers, fencing material, furniture etc.