Timber: Sources, Types & Properties
Where Timber Comes From
Timber is one of the oldest and most versatile materials available to designers, yet its origins matter as much as its properties. All structural timber begins as a tree; the species, the climate in which it grows and the way it is harvested all influence the qualities of the wood we eventually use. Designers must understand these origins to make responsible, informed material choices. The two principal categories are softwoods and hardwoods, though the names are misleading — balsa, classed as a hardwood, is lighter than most softwoods.
Softwoods: Common Species and Characteristics
Softwoods come from coniferous trees and account for around 80% of the world’s commercially harvested timber. They grow relatively quickly — typically 25–80 years to maturity — making them more sustainable and less expensive than most hardwoods. Key softwood species include:
- Scots pine (Pinus sylvestris) — pale yellow-brown with prominent grain markings and resin canals. Strong and relatively cheap; widely used for structural joinery, floorboards and carcassing.
- Spruce (Picea abies) — lightweight, pale cream with a fine, even grain. Used in guitar soundboards, aircraft construction and general interior joinery where a clean finish is needed.
- Larch (Larix decidua) — one of the few deciduous conifers; pale brown with a straight grain and natural resin that makes it more durable outdoors. Used in cladding, fencing and boat planking.
- Western red cedar (Thuja plicata) — reddish-brown, very lightweight and naturally resistant to rot and insect attack. Widely used for exterior cladding, shingles and greenhouses.
Hardwoods: Common Species and Characteristics
Hardwoods grow more slowly — oak may take 150 years to mature — so they are generally more expensive and face greater sustainability pressure. Their slower growth produces denser, tighter grain structures that often give superior durability and an attractive appearance. Key species include:
- Oak (Quercus robur) — pale brown to golden with distinctive ray figure; very hard, durable and resistant to moisture. Used in furniture, flooring, staircases and structural beams. Its tannin content can corrode iron fittings, so brass or stainless fixings are preferred.
- Ash (Fraxinus excelsior) — creamy white with a coarse, open grain and excellent elasticity. Ideal for tool handles, sports equipment (hockey sticks, oars) and steam-bent furniture components.
- Beech (Fagus sylvatica) — pale pink-brown with a fine, even grain; hard-wearing and easy to machine to a smooth finish. Used in workshop bench tops, furniture, toys and turned objects.
- Mahogany (Swietenia macrophylla) — rich reddish-brown, straight grain, works and finishes easily. Historically used in quality furniture and boat-building, though over-harvesting has made it expensive and ethically problematic unless FSC-certified.
- Balsa (Ochroma pyramidale) — extremely lightweight and weak; used in model-making, packaging inserts and core materials in composite sandwich panels.
Hardwood and softwood are botanical classifications, not descriptions of physical hardness. Balsa is technically a hardwood yet is the softest timber used commercially. In the exam, always justify your timber choice with a specific property (grain, durability, elasticity) matched to the product function.
Manufactured Boards
Manufactured boards are engineered sheet materials made from timber fibres, veneers or particles bonded with adhesives. They overcome many limitations of solid timber — available in large flat sheets, more dimensionally stable and often cheaper. The main types are:
- Plywood — odd number of thin wood veneers (plies) glued with grain directions alternating at 90°. Cross-grain construction gives high strength in all directions and resistance to splitting. Available in interior (UF glue) and exterior/marine grades (WBP phenolic glue).
- MDF (Medium Density Fibreboard) — wood chips steam-softened and mechanically defibrated into individual fibres, mixed with urea-formaldehyde resin and compressed under heat and pressure. Produces a perfectly smooth, consistent surface ideal for painting and router-cut profiles. Weak on edges; produces fine dust when cut.
- Chipboard (particle board) — wood chips and shavings bonded with synthetic resin. Lower cost and density than MDF; common in flat-pack furniture cores covered with melamine or veneer. Poor moisture resistance unless treated.
- Blockboard — solid softwood strips glued edge-to-edge then sandwiched between veneers (which may be softwood, hardwood or a thin sheet material) on each face. Strong in one direction; used in doors, work surfaces and shelving where rigidity over long spans matters.
- Hardboard — compressed wood pulp, smooth one side, rough the other. Thin and cheap; used as back panels in furniture and drawer bottoms.
- OSB (Oriented Strand Board) — large wood flakes compressed in alternating oriented layers, similar principle to plywood. Stronger and cheaper than chipboard; used in structural panels, roof decking and hoarding boards on construction sites.
Freshly felled timber (green timber) contains a high moisture content — sometimes over 100% in very wet species. If green timber is used directly, it will shrink unevenly as it dries in use, causing warping, splitting and joint failure. Seasoning reduces moisture content to match the environment in which the timber will be used (typically 10–14% for interior joinery, 18% or below for structural use).
Air seasoning stacks converted timber in open-sided sheds with spacer sticks (stickers) between each board to allow airflow on all faces. It is free of energy costs but slow — roughly one year per 25 mm of thickness — and cannot reduce moisture below the prevailing atmospheric humidity. Kiln seasoning uses heated chambers where temperature, humidity and airflow are controlled precisely; it can dry timber to any required moisture content within days to a few weeks. Kiln seasoning costs more but is standard in commercial production where consistent, low moisture content is essential.
Sustainability and the FSC
Deforestation is one of the most significant environmental challenges linked to timber use. Tropical hardwood logging destroys biodiversity hotspots, displaces indigenous communities and releases stored carbon. The FSC (Forest Stewardship Council) operates an international certification scheme; timber bearing the FSC label comes from forests managed to standards that ensure replanting, protection of ecosystems and fair treatment of workers. Manufactured boards often make better use of lower-grade timber and off-cuts, reducing waste. Specifying FSC-certified, locally sourced or reclaimed timber are all strategies that reduce the environmental footprint of a timber product.
Plywood’s cross-grain construction means it has near-equal strength in all directions and does not split easily along the grain — unlike solid timber. MDF has a perfectly smooth, knot-free surface ideal for painted finishes, but its urea-formaldehyde binders mean it produces hazardous fine dust when machined, requiring dust extraction and a suitable mask.
When selecting timber, designers consider both physical properties (what the material is like without doing anything to it) and working properties (how it responds to processing). Key physical properties include density, hardness, elasticity, natural colour and grain figure. Key working properties include how easily the timber can be cut, planed, turned, glued and finished. Ash scores highly on elasticity (returns to shape after bending), making it excellent for steam-bending. Oak’s hardness and density make it slow to work by hand but very durable. Beech machines to a very smooth surface, which is why it is used for workshop bench tops and children’s toys where a fine finish is needed without paint. MDF works well with routers because there is no grain direction to deflect the cutter.