Tactile properties and health benefits of wood

People form their perceptual perception of wood by feeling its warmth, coldness, hardness, softness, roughness and smoothness through touch and contact.

Wood is an ancient, environmentally friendly material. With economic development and rising consumer spending, people's expectations for their homes are becoming increasingly sophisticated. "Escape from concrete and return to nature" has become a primary goal for modern people in their pursuit of a natural and comfortable life. Consequently, humanity's utilization and appreciation of wood have reached unprecedented heights.

However, in our daily lives, what are the obvious advantages of wood compared to reinforced concrete and other modern materials? Let's discuss the tactile properties of wood.

In our daily lives, we experience different sensations when we come into contact with the surfaces of interior decoration materials, furniture, utensils, and everyday items. These sensations are triggered by our sense of touch. So, what is touch? Touch is a general term for mechanical stimuli such as contact, sliding, and pressure. Tactile organs are found throughout the human body. For example, the skin is located on the surface of the body. The free nerve endings in the epidermis allow us to sense temperature, pain, touch, and other sensations. This tactile sense allows us to clearly distinguish the softness and hardness of objects, the coldness and hotness of objects, and so on.

Li Kaifu, director of the Guangzhou South China Home Health Research Institute, professor and doctoral supervisor at South China Agricultural University, stated that people develop a sensory perception of wood through touch and contact, sensing its warmth, coldness, softness, hardness, roughness, and smoothness. These tactile properties make wood a highly sought-after material. These tactile properties are closely related to its structure, particularly its surface texture. Different wood species exhibit varying tactile properties.

01. Sense of cold and warm

When we touch the surface of a material, the temperature change at the interface stimulates our sensory organs, making us feel warm or cold. The sensation of warmth or cold is determined by the temperature change between the skin and the material, as well as the stimulation of heat perpendicular to the interface on the human sensory organs.

The perceived warmth or coldness of a wood surface is linearly correlated with the logarithm of its thermal conductivity. Because wood's thermal conductivity along the grain is generally 2-2.5 times greater than across the grain, a longitudinal section of wood feels slightly warmer than a transverse section. Wood's moderate thermal conductivity perfectly meets the needs of human activity, creating a warm and harmonious experience and thus achieving health benefits. This is one of the key reasons why wood flooring is so popular, as it significantly improves the living environment.

As can be seen in the figure above, the perceived warmth or coldness of a wood surface is inversely proportional to its thermal conductivity. Wood's thermal conductivity influences the density and velocity of heat flux through the wood, affecting the temperature and temperature fluctuations at the skin-wood interface, ultimately affecting the perceived warmth or coldness of the wood.

This graph shows that the temperature sensation of the human skin surface changes differently when it comes into contact with different wood species and materials. The finger temperature after contact with the test piece varies depending on the material used, with the temperature changing in different ways. For polystyrene foam and balsa wood, the temperature increases very slowly, while for concrete and high-density woods like oak, the temperature decreases slowly. For medium-density woods like larch, the temperature remains relatively stable.

02. Soft and hard feeling

The surface of wood has a certain hardness, which varies depending on the species. Generally, most coniferous wood is less hard than broadleaf wood, and the hardness of wood from different parts and sections of the same species varies greatly, resulting in some wood feeling soft and light to the touch, while others feel hard and heavy. Studies have shown that the average end surface hardness of wood is 53.5 MPa, ranging from 13.1 to 165 MPa. The average hardness of coniferous wood is 34.3 MPa, ranging from 19.2 to 63.8 MPa; the average hardness of broadleaf wood is 60.8 MPa. This hardness of wood is right in the middle of the hardness value or slightly harder, which makes people feel comfortable during use. At the same time, wood has good impact resistance, so laying wooden floors and using wooden furniture can give people a sense of security.

03. Roughness

Roughness refers to the tactile stimulation of roughness and friction. Generally speaking, the roughness of a material is determined by the degree of minute surface irregularities. Even after planing or sanding, wood surfaces are not completely smooth due to the exposed cells on the cut surface, resulting in a moderate roughness. This property also results in a moderate coefficient of friction, with little difference between the static and kinetic coefficients of friction. Consequently, wood flooring offers a superior feel to walking on than plastic tiles, especially when the moisture content of the floor surface fluctuates; wooden floors remain smooth and maintain a pleasant feel.

To sum up, the overall sense of cold and warm of wood is relatively mild, and the softness, hardness and roughness are moderate. The perfect tactile characteristics give people appropriate stimulation, making people feel comfortable and playing an important regulatory role in people's psychology and health.