Cork, or to be more precise, the bark of the cork oak tree, has exceptional properties. The bark of the cork oak tree has a unique cellular structure composed of tiny cells. It is an amazing material whose properties cannot be achieved or surpassed by modern technologies. The cork oak tree grows in the Western Mediterranean, with Portugal and Spain being the largest cork suppliers.
The properties of cork arise from its structure and the chemical composition of its extremely strong and flexible cell membranes, which are characterized by moisture resistance and air impermeability. Cork is harvested without causing harm to the tree. Trees regenerate their bark in just a few years, so the loss is not critical for them. On average, the bark is harvested approximately 11 times over the tree’s 150-year lifespan.
It is important to note that the bark is removed without the use of any machinery; it is stripped by hand at the right moments when the tree is ready to shed it. Therefore, cork is considered an environmentally friendly material.
Under an electron microscope, it can be seen that each cell has the shape of a 14-sided polyhedron, and the interior of the cell is completely filled with a gas mixture.
Since approximately 89% of the cork tissue consists of gas, the density of cork is extremely low, around 0.12-0.20, indicating a huge disparity between the volume and weight of the material.
Thanks to its cellular structure, cork has volumetric memory, which means it can regain its shape after being subjected to physical pressure on its surface.
Some of the unique and valuable properties of cork include:
Lightness: Cork is very lightweight and can float on water. Throughout thousands of years, this property has remained its most obvious and remarkable characteristic. The material is very light (104-120 kg/m³).
Elasticity and resilience: The cellular membranes of cork are extremely flexible, making it elastic. It can return to its original shape even after deformation.
These and other qualities explain why cork has become an essential material for making bottle stoppers. These physical qualities enable cork to tightly seal the neck of a bottle. When subjected to strong pressure, the gas inside the cells compresses, significantly reducing its volume. When the pressure is released, the cork immediately returns to its original shape and volume, leaving no trace of significant deformation.
The familiar wine cork is a clear demonstration that neither liquids nor gases are absorbed into this material. It does not promote mold growth or decay and possesses long-lasting volumetric memory.
Impermeability: The presence of suberin (a complex mixture of fatty acids and organic alcohol) makes cork impermeable to liquids and gases. As a result, it does not deteriorate, making it one of the best sealing materials.
Insulating and fire-resistant qualities: Cork’s value is also determined by its low thermal conductivity, sound absorption, and vibration isolation. This is due to the fact that the gas elements it contains are enclosed in tiny, impermeable chambers, isolated from each other by moisture-resistant material. This property makes cork one of the best natural thermal and sound insulating materials.
Wear resistance: Cork is highly resistant to wear and has a high coefficient of friction. Its cellular structure minimizes the effects of impact or friction compared to other solid surfaces.
Hypoallergenic properties: Cork does not absorb dust, which helps protect against allergies and does not pose a threat to people with asthma. It also maintains a consistent structure, ensuring the effectiveness of this material.
Interesting fact: Did you know that the walls of space capsules are covered with cork? More specifically, the same ones used to bring astronauts back to Earth. The reason is that cork significantly reduces the levels of harmful electromagnetic and radioactive.
This traditional satellite of wine bottles is so good that it saves astronauts’ lives even in situations when the metal walls of the capsule start melting and flowing. Thermal insulation? Absolutely! When the external walls of the cork covering start burning, the metal underneath remains as cool as the surface of the Earth! Scientists have proven that the cork covering reliably protects against anomalous fields, reducing the effect of geopathogenic zones by 75-80 percent.