What’s Cork?

The cork oak (Quercus Suber L) is the tree that provides cork, which is its bark. It is the only tree whose bark regenerates. Harvested after 25 years’ growth in cycles of 9 years, the cork oak presents us with a natural raw material with unique characteristics, cork.

What makes it unique is the honeycomb structure of its microscopic cells filled with a air-like gas and coated mainly with suberin and lignin.

It’s chemical composition as a material is the following:
1.suberin (45%)
2.lignin (27%)
3.polysaccharides (12%)
4.ceroids (6%)
5.tannins (6%)

Suberin, being the main component of cork, is 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, etc.

The cells grouped in a characteristic alveolar structure are the essence that defines cork. A cubic centimeter of cork contains nearly 40 million cells, arranged in rows perpendicular to the cork oak trunk, giving it its capacity to float, insulate and re-expand after compression.

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 measuring 20 or as little as 10 micrometres. All these cells are filled with a mixture of gases similar to air. A plank of cork contains nearly 60% gaseous elements, which explains its extraordinary lightness. These small cushions of air are what 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.

Cork is natural and recyclable, and the cork oak tree grows without the need of chemical substances or irrigation, although recent research confirms that irrigation can allow a short time between harvests.

The cork oak, grown in forests or groves, lives up to 200 years. Cork oak bark grows in around of 1.5 mm each year retaining huge amount of CO2 from the atmosphere during his growth. A forest of cork oak trees is usually called a Montado.

The cork is harvested by specialized professional with traditional methods during the spring and summer period, usually May up to august.