CourseWiki/Materials and Manufacturing Processes/Wood

Wood Structure and Species

Read tree structure, distinguish botanical groups, and choose species for their properties rather than their names.

Wood belongs to the Wood & Composites family

Wood is a cellular material whose properties depend on direction. Long cells run mainly along the trunk; their arrangement helps explain why a board carries loads and splits differently along and across its grain.

In the material-family model, wood belongs to Wood & Composites. Engineered wood products combine veneers, strands, particles, or fibers with binders. These products are why composites share this family. See Engineered Wood Products for the product choices; the material families and manufacturing process categories are foundation topics.

What makes the cell walls work together?

Cellulose reinforces the cell wall, while lignin and hemicelluloses help form its surrounding structure. This is a useful natural-composite analogy, but a tree is more complex than fibers suspended in glue. Cell arrangement, moisture, knots, and grain direction all affect a real board.

Read a trunk from bark to heartwood

Trunk cross-section: outer bark, inner bark, thin cambium, sapwood, heartwood, central pith, growth rings and radial rays.

Bark: Outer bark protects the tree. Inner bark carries sugars made by the leaves.
Cambium: A thin growing layer produces new wood toward the inside and new inner bark toward the outside.
Sapwood: The outer wood conducts water and contains living storage cells. Many of its conducting cells are already dead at maturity.
Heartwood: Older inner wood no longer conducts water. Deposits can change its color and decay resistance; heartwood is not automatically stronger or decay-resistant in every species.
Pith and rays: The pith marks the central stem tissue. Rays run radially across the wood and contribute to storage and transport across the trunk.

A growth ring records a growth cycle. In many temperate trees, earlywood develops earlier in the season and latewood later. Their cells differ in size and wall thickness, creating visible bands. Ring contrast varies by species; ring width alone is not a strength grade.

Hardwood and softwood describe the tree, not its hardness; Practice

Hardwood and softwood describe the tree, not its hardness

Hardwoods come from angiosperm trees; softwoods come from gymnosperm trees, commonly conifers. Leaf shedding is not the defining test: some hardwood trees are evergreen, and some conifers shed their needles.

Balsa is a very soft hardwood. Southern yellow pine is a softwood but can be much harder than balsa. Ask about the species and the property you need, rather than treating the category name as a test result.

How the cell structure differs

Most commercial hardwoods have vessels, visible as pores in end grain, along with supporting fibers. Softwoods rely mainly on long cells called tracheids for support and water transport. These differences influence appearance and processing, but do not make every member of either group behave alike.

Practice: balsa Practice: yellow pine

Match common species to the job

These are typical starting points, not grades or guaranteed design values. Inspect the actual board for grain, knots, moisture, and defects.

Common North American woods and familiar uses
Species or group	Typical character	Common uses
Pine	Varies widely: eastern white pine is relatively light and soft; southern yellow pines are generally denser.	Trim, construction lumber, furniture parts.
Yellow-poplar (tulip-poplar)	Relatively soft hardwood; easy to machine and often painted. Not the same tree as aspen.	Painted trim, cabinet parts, concealed furniture parts.
Red oak	Hard, prominent open pores and grain.	Flooring, furniture, cabinetry.
White oak	Hard, prominent rays; heartwood is generally more decay-resistant than red oak heartwood.	Furniture, flooring, cooperage such as barrels.
Hard maple	Hard, fine texture, good wear resistance.	Flooring, work surfaces, furniture.
Black walnut	Dark heartwood and valued figure; sapwood is lighter.	Furniture, cabinetry, decorative veneer.
Black cherry	Fine texture; heartwood darkens with exposure.	Furniture, trim, veneer.
Yellow birch	Hard, fine texture; often used as veneer.	Cabinetry, furniture, plywood faces.

Continue with Grain and Moisture Movement before selecting a board by appearance alone.

Further reading on wood properties and products

Reference resources

Appears in

DET 130 DET Wood as a Material