Heartwood vs Sapwood

Heartwood and sapwood are not two different woods. They are two different roles inside the same tree.

This guide explains what sapwood does, what heartwood is, and what the heartwood/sapwood divide changes in real woodworking decisions.

What Sapwood Is

Sapwood is the living outer wood of the tree.

Its main job is to move water and nutrients up from the roots.

Common traits of sapwood:

• usually lighter in colour
• higher moisture content when freshly cut
• more biologically “active” when the tree is alive

Because sapwood is used to transport fluids, it tends to be more open to things that move through wood.

What Heartwood Is

Heartwood is older wood in the centre of the tree.

Over time, the tree stops using this zone for transport.

Instead, the cells become blocked and the tree often deposits chemicals into the wood. These deposits are called extractives.

Common traits of heartwood:

• usually darker in colour (though not always)
• often has higher natural durability
• may have different smell, taste, or working behaviour depending on species

Heartwood is not “dead” in a structural sense. It is still the bulk of the tree’s strength. It is just no longer part of the tree’s plumbing.

Why the Colour Difference Happens

Many species develop a strong contrast because heartwood accumulates extractives.

These can change:

• colour
• decay resistance
• how the wood reacts to finishes

Some species show a dramatic difference (for example, many cedars and yews).

Other species show very little difference, so the heartwood and sapwood can be hard to tell apart.

Durability: The Big Practical Difference

In many species, heartwood is more rot resistant than sapwood.

That is because the extractives can inhibit fungi and insects.

Important practical point:

• Sapwood is usually not durable outdoors unless treated, even if the species is considered durable.

This is why outdoor timber specs often talk about “heartwood only” for certain applications.

Strength and Movement: What Usually Does Not Change Much

Heartwood and sapwood are made from the same basic cell structure, so:

• strength differences are often small compared to differences between species
• shrinkage and swelling behaviour is usually similar within the same board

In practice, moisture content, grain orientation, and drying quality have a bigger impact on movement than whether a piece is heartwood or sapwood.

What It Means for Woodworking

Appearance decisions

Sapwood can be:

• a feature, if you like contrast
• a defect, if you want a uniform colour

Outdoor decisions

If you are building for exterior use, check:

• whether the species heartwood is durable
• whether sapwood needs treatment or exclusion

Finishing decisions

Heartwood and sapwood can absorb stain and finish differently, which can create blotching or visible banding if you are not expecting it.