Sapwood and Heartwood

What is sapwood or heartwood?

When people think of wood, they often imagine a uniform material. In reality, however, a tree trunk consists of different zones that vary in their characteristics, depending on the tree species. In general, we distinguish between sapwood and heartwood, each fulfilling important functions in the tree and bringing its own specific properties for woodworking.

Sapwood & heartwood | Feeding always takes place via the sapwood. Every year, one annual ring of sapwood becomes heartwood. | Photo © by Hugo Kämpf

Expkanation and Differences

Sapwood: Sapwood is the younger, physiologically active zone of the tree, located just under the bark. This layer stores water and nutrients and transports them up into the crown. Sapwood is typically lighter in color. Because it is part of the active sap flow, it is generally moister and softer than heartwood.

Heartwood: Further inside the trunk, usually darker in color, lies the heartwood. It is no longer physiologically active and primarily serves structural support for the tree. Since many species do not conduct water and nutrients through heartwood, it generally contains less moisture, which has a positive effect on its strength and durability.

Mature Wood: Some trees develop what is known as mature wood (for example, spruce or linden) instead of clearly defined heartwood. This internal zone may be only slightly darker than the sapwood but still shows characteristics similar to true heartwood. It is often referred to as “transitioned” inner wood.

Advantages and Disadvantages

Sapwood – The “Supplier”: Sapwood actively absorbs water and nutrients and therefore has a higher moisture content. It is usually lighter and softer, which can be aesthetically appealing in certain situations. However, it is less resistant to pests and the elements, which is why it is rarely used outdoors. When moisture levels change, sapwood tends to swell and shrink more, increasing the risk of cracks and distortions.

Heartwood – The “Strong One”: Heartwood is characterized by its stability and lower moisture absorption. Many heartwoods contain tannins or resins that naturally protect against fungi and pests. It is often darker and exhibits striking color tones valued in furniture and interior design. Nonetheless, it can be more challenging to impregnate or work with because it is denser than sapwood.

Heartwood Trees and Sapwood Trees

Sapwood Trees: In sapwood trees, the entire cross-section is involved in transporting water and nutrients, resulting in minimal visual or moisture-related differences between the outer and inner wood zones. Examples include birch, alder, and maple. The wood in these species remains relatively light in color across the entire trunk and maintains the general characteristics of sapwood throughout.

Heartwood Trees: Many species form a darker, inactive heartwood in the trunk interior, which clearly differs from the outer sapwood layer. Common heartwood trees include pine, larch, oak, walnut, rosewood, and teak. There is also a special group known as mature wood trees—for instance, spruce and linden—where an internal zone develops but shows little color difference from the sapwood.

Processing and Application
Live edge table with sapwood | Photo © by Hugo Kämpf

Use of Sapwood: Sapwood is often utilized where its lighter color and pronounced grain are desired for artistic or design purposes. Some woodworkers like the contrast between the pale sapwood and the darker heartwood to create furniture with a striking appearance.

However, sapwood is less suitable for outdoor or heavily used structures due to its lower resistance. Its relatively high moisture content increases the risk of cracks and warping during drying. Careful, gentle drying is essential to prevent stress in the wood.

Oak sawn timber with sapwood and heartwood | Photo © by Hugo Kämpf

Use of Heartwood: Heartwood is therefore ideal for load-bearing components and long-lasting furniture such as live edge tables, which should remain dimensionally stable for years. Nevertheless, professional drying is also essential for heartwood, as stress cracks or deformation can occur if the moisture values are not precisely controlled before installation.

Drying and Storage: Whether sapwood or heartwood is used significantly impacts the chosen drying method and subsequent storage. Sapwood dries faster but carries a higher risk of cracking, since its higher water content leads to a rapid release of moisture.

Heartwood is less prone to warping but likewise requires a slow and even drying process to minimize uneven stresses. In both cases, maintaining stable climatic conditions during storage is crucial for preparing the wood for further processing.

Surface Treatment and Care: Sapwood and heartwood differ mainly in terms of pore structure and natural contents, which affects how they should be treated and cared for. Sapwood readily absorbs oils and stains but loses its protective layer more quickly because it rapidly takes in moisture. Heartwood can be more difficult to impregnate but often benefits from its inherent protective substances, such as resins or tannins.

Thorough surface preparation - through sanding or the use of suitable primers - improves the absorption of coatings in both types. Regular re-treatment helps the wood maintain its original appearance and remain less susceptible to environmental influences.