Cork is the bark of the cork oak. It is a 100% natural plant tissue consisting of a hive of microscopic cells containing a gas identical to air and coated primarily with suberin and lignin. It has a range of applications associated with its attributes that no technology has yet managed to emulate, match or exceed.
It is a 100% natural raw material, that is 100% reusable and 100% recyclable, extracted from cork oaks without harming the normal development of the species and without damaging the tree. The extracted cork is 100% harnessed. Once processed, into stoppers for example, cork can also re-enter the production process. The cork stoppers can be recycled by shredding. The granules resulting from this process can be used in other products, such as shoes, cladding panels, fishing buoys.
Over 50% of its volume is air, which makes it very light. It weighs just 0.16 grams per cubic centimetre, and it can float.
Impermeable to liquids and gases
It is totally impermeable to liquids and practically impermeable to gases, thanks to the suberin and cerin present in the composition of cork cells. Its resistance to moisture allows it to grow old without deteriorating.
Elastic and compressible
It can be compressed to around half its thickness without losing any flexibility, and it decompresses, recovering its initial shape and volume, as soon as it ceases to be compressed. This flexibility is given by its airtight cells containing a gas mixture similar to air. It is the only solid that when compressed on one side does not increase in volume on the other axis. It is able to adapt to variations in temperature and pressure without suffering variations, due to its elasticity.
Excellent thermal and acoustic insulator
The 40 million cells in each cubic centimetre of cork act as a real decibel absorber, making it an excellent sound and vibration insulator. Its molecular structure allows it to absorb heat and retain it for a long period of time.
The slow combustion of cork makes it a natural fire retardant and a kind of barrier against fires. Cork burns without a flame and does not emit toxic gases during combustion.
Antistatic and anti-allergic
It does not absorb dust and prevents the appearance of mites and, therefore, contributes to protection against allergies.
Cork is resistant to wear, thanks to its honeycomb structure, which makes it less affected by impact or friction than other hard surfaces.
Cork cells have a pentagonal and sometimes hexagonal prism shape. The height of one of these tiny prisms is around 40 to 50 micrometres (thousandths of a millimetre). The smallest cells measure 20 or even 10 micrometres. On average, there are around 40 million cells in each cubic centimetre of cork, or approximately 800 million cells in a single cork stopper.
The numerous qualities of cork can only be understood following a meticulous analysis of its chemical composition, to identify its various components and their average values:
The main component of cork is suberin, a mixture of organic acids that coat the walls of the cork cells, preventing the passage of water and of gases. The properties of suberin are notable: it is practically infusible and is insoluble in water, alcohol, ether, chloroform, concentrated sulphuric acid, hydrochloric acid, etc.
The cells grouped in a characteristic alveolar structure are the essence that defines cork. A cubic centimetre of cork contains nearly 40 million cells, arranged in rows perpendicular to the cork oak trunk.
Each cell is shaped like a tiny pentagonal or hexagonal prism, the height of which is no more than 40 to 50 micrometres (=thousandths of a millimetres). The smallest cells measure 20 or as little as 10 micrometres. Whatever their size, all the cells are filled with a mixture of gases similar to air. Around 60% of a plank of cork is composed of gaseous elements, which explains its extraordinary lightness. The combination of these small cushions of air make cork so remarkably compressible. At the same time, suberin makes the walls of the cork cells impermeable and therefore airtight. The gas they contain cannot escape, which is the reason for the elasticity of the tissue and also its low thermal conductivity. It also has an average density of about 200 kg/m3.