What is the difference between heartwood and sapwood?
The Wood Guide · Calculating with wood
Wood knowledgeHeartwood and sapwood
Saw through a trunk and you see two zones: a dark core and a lighter outer edge. The difference decides how long a board lasts.
- Heartwood = dead, durable
- Sapwood = living, perishable
- Determines the EN 350 class
Two zones in one trunk
Saw through a trunk and you see a dark core and a paler outer band. That difference decides how long a board lasts.
Click a chapter or use the arrows · schematic drawings, not to scale.
Heartwood and sapwood in brief
Both belong to the same trunk, but they play a very different role in the living tree — and that carries through into the timber you buy.
Sapwood is the living part: the outer rings that carry sap from the roots to the crown. It contains a lot of moisture, plenty of nutrients and no protective substances. That is exactly why it attracts fungi and insects.
Heartwood is the inner, retired part. As a tree grows, the innermost cells die and the tree fills them with substances that make the wood denser, darker and better protected — tannins in oak, oils in teak. That is what makes a wood species durable.
So the colour boundary is not an aesthetic matter but a chemical one. What you see is the difference between wood that is defended and wood that is not.
When a wood species is given "durability class 1" under EN 350, that applies only to the heartwood. The sapwood of that same tree is usually class 5. So a teak board with a wide band of sapwood holds out much less long outdoors than its class promises.
- Position
- heartwood in the centre, sapwood on the outside
- Colour
- heartwood darker, sapwood lighter
- Moisture content
- heartwood lower, sapwood higher
- Durability
- heartwood durable, sapwood almost always class 5
- Function
- heartwood supports, sapwood carries sap
- Pressure treatment
- sapwood absorbs well, heartwood hardly at all
To be fair: a lot of cheap garden timber contains a sizeable band of sapwood, because that way more usable boards come out of one trunk. You cannot see it in the photo, and it is rarely mentioned in the description.
What exactly differs
| Characteristic | Heartwood | Sapwood |
|---|---|---|
| Position | In the centre of the trunk | On the outside, under the bark |
| Colour | Darker | Lighter |
| Function in the tree | Supports, gives strength | Carries sap and nutrients |
| Living tissue | No, dead cells | Yes |
| Moisture content | Lower | Higher |
| Natural durability | More durable | Less durable, usually class 5 |
| Hardness | Harder | Softer |
| Uptake of preservative | Poor | Good |
What you do with it
For garden furniture
Ask for timber with as little sapwood as possible. A light, clearly different edge along the board is sapwood — it decays first and attracts insects.
For pressure treatment
Here it is the other way round: sapwood is actually an advantage. It absorbs the preservative well, while heartwood hardly lets it in. Spruce has a lot of sapwood, which makes it excellent for pressure treatment.
When buying
Look at the end grain. You see the transition there straight away; a wide light edge is a warning.
When it weathers
Weathered wood turns grey all over, so the colour difference disappears on the outside. Judge it on the end grain, or before it goes outdoors.
Some species — beech, maple, spruce — do not form clearly coloured heartwood. That does not mean they have no heartwood, but that the difference can hardly be seen with the naked eye. In oak, teak and padauk it is very pronounced.
Frequently asked questions about heartwood and sapwood
Is sapwood useless?
Certainly not. For indoor uses it is fine, and for garden timber that is to be pressure-treated it is actually desirable, because it absorbs the preservative well. Only in untreated outdoor timber is it a weak spot.
How do I recognise sapwood?
Does a durability class apply to the whole board?
No. The class under EN 350 applies only to the heartwood. Sapwood of almost every species falls into class 5.
Why is heartwood darker?
Because the tree fills dead cells with substances such as tannins, resins and oils. They colour the wood and protect it against fungi and insects.
Heartwood and sapwood in perspective
One look at the end grain tells you more about service life than the entire product description.
Have a question about your project? Just ask — we're happy to help.
Photos via Wikimedia Commons: Laburnum — Per Grunnet, CC BY-SA 4.0 · Prunus domestica — Mussklprozz, CC BY-SA 3.0