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Material World
Material · Processed natural

Wood

A cellular composite of cellulose and lignin — the only major structural material that is grown rather than extracted.

Construction material Fuel

Wood is a natural composite: cellulose fibres, which are strong in tension, embedded in lignin, which resists compression and holds the fibres apart. The arrangement is the same principle as fibreglass, arrived at several hundred million years earlier.

Its defining characteristic is that its properties depend on direction. Wood is strong along the grain and weak across it, shrinks and swells across the grain and barely at all along it, and splits readily in one plane. Almost every traditional woodworking technique — and every failure of a badly designed wooden object — follows from that anisotropy.

Processing

Between the tree and the material there is seasoning. Green wood contains a great deal of water, both free in the cell cavities and bound in the cell walls, and it is the bound water that matters: as it leaves, the wood shrinks, and if it leaves unevenly the piece cups, bows or splits.

Air drying takes months to years; kiln drying takes days and allows the moisture content to be controlled to a target. Wood then continues to move with humidity for the rest of its life, which is why joinery is designed to allow it rather than to prevent it.

Uses

Structural timber, joinery, flooring and furniture are the visible uses. Engineered products now account for a great deal of the volume: plywood, laminated veneer and cross-laminated timber redistribute the grain so that the weakness across it is designed out, which is what makes tall timber buildings possible.

Wood is also the feedstock for paper and for a growing range of cellulose-derived materials, and it remains a primary fuel. As a structural material it is unusual in storing carbon rather than emitting it during manufacture.

Environmental impact

Wood is renewable in a way no mineral material is, and a growing forest absorbs carbon dioxide that remains locked in the timber for the life of the product. Substituting timber for concrete or steel in construction reduces embodied emissions substantially.

That advantage depends entirely on how the wood is grown. Timber from managed forest replanted after harvest behaves as described; timber from clearance of old-growth or tropical forest does not, because the carbon released and the habitat lost are not recovered on any useful timescale.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

is used in

  • Construction — industry · structural timber, joinery and engineered panels
  • Pencil — object · incense cedar traditionally, split into two slats and glued around the core

is a source for

  • Paper — material · pulped mechanically or chemically; most harvested wood by mass ends here
  • Resin — material · tapped from the living trunk — from the bark and sapwood rather than the wood itself, which is why a tree can be worked for decades and still be felled for timber afterwards
  • Jet — material · araucarian driftwood that floated out to sea, waterlogged, sank into anoxic Jurassic seafloor mud and was compressed without ever being heated enough to go past lignite
  • Charcoal — material · heated without air until the water and the volatile three quarters have gone, leaving a carbon skeleton that still holds the shape of the wood

is an input to

  • Kraft pulping — process · as chips, cooked until the lignin dissolves and the cellulose fibres separate
  • Tanning — process · as bark rather than timber: vegetable tanning uses tannins extracted from bark, wood and leaves, and it is the older of the two routes by several thousand years
  • Pyrolysis — process · and what comes off was the point for most of history: methanol, acetic acid and acetone all came from wood distillation before petroleum

is an alternative to

  • Steel — alloy · in building frames. Engineered timber has taken back mid-rise construction from steel on carbon-footprint grounds, having lost it on fire and span a century earlier
  • Concrete — material · in building frames, where the argument has moved from cost and fire to embodied carbon — and engineered timber has taken back mid-rise on that ground
  • Plywood — material · strong in both directions and dimensionally stable where a board is neither, and it needs large straight logs and a synthetic adhesive to be either

is used as

  • Structural engineering — application · the oldest structural material still in mainstream use, and returned to mid-rise construction by engineered timber

is a component of

  • Plywood — material · peeled into veneer on a lathe, which is how a panel wider than any board is made from a log

was succeeded by

  • Glass fibre composite — material · in small boat construction, and completely: a moulded hull needs a mould and unskilled labour where a wooden one needs skill and continual maintenance

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Wood back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Downstream — what it becomes

  • Wood → is a source for (heated without air until the water and the volatile three quarters have gone, leaving a carbon skeleton that still holds the shape of the wood) → Charcoal → is an input to (as both the fuel and the reducing agent, and it smelted every metal humanity had until coke — which is why ironworks were built in woods rather than at the ore) → Smelting → produces (as blister copper, refined electrolytically afterwards) → Copper → is a component of → Bronze → is associated with (the alloy the period is named for) → Bronze Age complete chain
  • Wood → is an input to (as chips, cooked until the lignin dissolves and the cellulose fibres separate) → Kraft pulping → produces (as tall oil rosin from the black liquor — a by-product of making paper, and now a larger source than tapping) → Resin → is used in (as the flux in rosin-cored solder wire: it strips the oxide off copper at soldering temperature so the solder can wet the metal, and the smell of soldering is the smell of pine) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Wood → is a source for (tapped from the living trunk — from the bark and sapwood rather than the wood itself, which is why a tree can be worked for decades and still be felled for timber afterwards) → Resin → is used in (as the flux in rosin-cored solder wire: it strips the oxide off copper at soldering temperature so the solder can wet the metal, and the smell of soldering is the smell of pine) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Wood → is a component of (peeled into veneer on a lathe, which is how a panel wider than any board is made from a log) → Plywood → is associated with (the de Havilland Mosquito was a plywood aeroplane, and it was fast because of it) → The wartime materials programmes complete chain
  • Wood → is an input to (and what comes off was the point for most of history: methanol, acetic acid and acetone all came from wood distillation before petroleum) → Pyrolysis → produces (the kiln burns a small fraction of the wood to supply the heat that pyrolyses the rest) → Charcoal → is an input to (as both the fuel and the reducing agent, and it smelted every metal humanity had until coke — which is why ironworks were built in woods rather than at the ore) → Smelting → produces (as blister copper, refined electrolytically afterwards) → Copper → is a component of → Bronze
  • Wood → is a source for (pulped mechanically or chemically; most harvested wood by mass ends here) → Paper → is used as (cartons and cases, and the material most plastic packaging is now being asked to justify itself against) → Packaging

These are the most distinct paths onward. Wood ends up in others besides.