Module 1 · What wood is, and how it is measured

Softwood and hardwood: the distinction that is not about hardness

Level 1 · Foundation 9 min read 4 questions

The two great divisions of commercial timber are botanical, not mechanical. Some hardwoods are soft and one important softwood is hard, and the naming has confused buyers for a century.

Every commercial timber species falls into one of two groups. Softwoods are conifers - gymnosperms - which bear seeds in cones and mostly keep their needles. Hardwoods are broadleaved flowering trees - angiosperms - which mostly shed their leaves in temperate climates. That is the whole of the distinction. It says nothing directly about how hard the wood is.

Why the distinction still matters commercially

Even though it does not predict hardness, the division predicts almost everything else about how a species is grown, sold and used.

The difference in rotation length is the most important line in that table. A softwood plantation is a crop with a human planning horizon. A walnut or white oak sawlog is the product of a century, which means nobody alive planted it for the market it is being sold into. Hardwood supply cannot respond to price at all on any timescale that matters, and the entire hardwood market follows from that.

The structure of a log

Bark

Outer protective layer. At the mill it is removed first and sold - lesson 10 covers where it goes.

Cambium

The thin living layer just under the bark where growth happens. Everything inside it is dead tissue.

Sapwood

The outer wood, still conducting water. Usually paler, and in most species less durable and more prone to staining.

Heartwood

Inner wood that has ceased conducting and become chemically altered. Usually darker, more dimensionally stable and, in some species, markedly more decay resistant - which is the entire commercial case for western red cedar, redwood and black locust.

Growth rings

One per growing season in temperate species, each with faster, lighter earlywood and denser, darker latewood. Ring spacing is a direct read on growth rate, and in softwoods tighter rings generally mean denser, stronger wood.

Rays

Radial tissue running across the rings. In oak they are large, and cutting to expose them produces the quartersawn figure that the trade pays for.

Moisture, the property that ruins everything

Freshly cut wood is full of water - green wood can weigh far more than the same wood dry, which is why pulpwood is sold by weight and why haul economics depend on how long a log has been sitting. As wood dries below roughly 30% moisture content, it begins to shrink, and it shrinks unequally: much more around the rings than across them, and almost not at all along the grain.

That inequality is the cause of nearly every defect a woodworker fights. Cupping, bowing, twisting, checking and splitting are all differential shrinkage. It is why lumber is dried before it is sold for most uses, why the sawing pattern in lesson 9 matters, and why wood delivered at the wrong moisture content for its destination will move after installation however good the board looked.

Density and hardness

Within either group, the property that predicts most mechanical behaviour is density. Denser wood is generally stronger, stiffer, harder and heavier, holds fasteners better, machines differently and burns hotter. The trade's usual hardness measure is the Janka test: the force needed to embed a steel ball half its diameter into the wood.

Read the table and the botanical point makes itself: four softwoods are harder than three of the hardwoods below them, and the softest wood in the list is a hardwood. Hardness is also not the only thing a buyer wants. A flooring buyer wants hardness; a carver wants basswood precisely because it is soft; a pattern maker wants stability above everything.