The cork oak is a unique species in the world, producing a very thick bark of uniform structure which grows spontaneously when the tissue covering the trunk dies.
The bark of this tree - in common parlance "cork" - is a cork tissue constantly formed during the life cycle of these trees as a result of the constant increase in the cross section of their trunks. This tissue, visible under the microscope, is constructed of closed microcells whose shape recalls that of polyhedrons with 14 faces and intercellular spaces completely filled with a gaseous mixture almost identical to the air of the environment surrounding the tree. In 1 cm3 of said tissue there are more than 42 million of these 14-sided cells. Their chemical composition includes: suberin (45%), lignin (27%), cellulose and polysaccharides (12%), tannin (6%), wax (6%) and other substances (5%).
Lightness:
the air trapped in the microcells of cork constitutes 90% of its volume and about 50% of its weight, its specific weight is in the range of 180-250 kg/m3. It is therefore a material five times lighter than water, and since it does not absorb water, it is practically unsinkable.
Impermeability:
cork owes this characteristic to an increased presence of suberin. The suberin content is 39-45% of the cork weight. This substance has properties that waterproof the structure and also reinforces and thermally insulates the latter.
Chemical neutrality:
cork is chemically inert. Its structure is not only impermeable to liquids and gases, but also in contact with them, does not react chemically and is not subject to destruction. Cork also retains flavor neutrality and odorless character, as well as it does not absorb odors.
Biological corrosion:
corrosion is due to favorable conditions for humidity and putrefaction. The increase in resistance to biological corrosion is due, among other things, to the presence in its composition of tannins and an absence of protein substances sensitive to decomposition. It also retains mold resistance. Its surfaces and structures do not constitute a nutrient medium for fungi and moulds, nor do they create the conditions for colonization.
Thermal: the coefficient of thermal conductivity of this material is 0.037-0.040 W / (mK). In addition to this advantage, it is interesting to note the very high value of the specific heat. This value results in a high thermal inertia of the cork. Unlike other materials, it retains insulating properties over a very wide temperature range. In this regard, its properties are much higher than, for example, polystyrene, which evaporates under the influence of high temperature. Due to the low conductivity, cork is always pleasant to the touch, because it neither lets through nor absorbs heat. This material also has the property of stabilizing air temperature and humidity.
Acoustic:
cork can absorb 30 to 70% of sounds in the frequency ranges of 400 to 4000Hz. Its structure and flexibility allow you to simultaneously weaken air and shock sounds and eliminate the area of acoustic bridges. Cork, thanks to its specific structure, absorbs acoustic waves and vibrations (it does not transfer vibrations, but it dampens them).
Fire resistance. Cork retains Euroclass E fire resistance. However, this detail depends on many factors. As a general rule, cork sheets, due to the high thermal inertia, are fireproof.
Flexibility:
cork's cell membranes are very flexible, making them compressible and elastic, and once the pressure is removed, the cork returns to its original shape. When cork is exposed to high forces, the gas in these cells compresses, and its structure reduces its volume. Once the pressure is removed, the cork returns to its original shape.
Anti-electrostatic:
the cork surface does not accumulate electrical charges, in other words, the cork does not become electrified, so there is no phenomenon here of attracting and absorbing dust. Cork surfaces are therefore easy to clean. For allergy sufferers and asthmatics, the use of cork in areas used by them means that contact with allergens is limited.
Aging:
cork is ranked among the most durable organic materials. Practically it is not subject to the aging process and, despite the passing years, even without undergoing an impregnation intervention, it does not lose its properties, and even some environments preserve them (sea water, etc.. ).
Machining:
cork can be machined with simple cutting and scraping tools. It adheres well to uneven surfaces as it adapts its shape.