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Cork properties

 

Cork Cells © by APCOR Cork Cells © by APCOR

A reminder of the unique properties of cork which no other natural or artificial product has yet been able to emulate or improve, is always welcome:

  1. light
  2. impermeable to liquids and gases
  3. elastic and compressible
  4. excellent thermal and acoustic insulator
  5. slow burning 
  6. highly abrasion resistant

However these numerous qualities can only be understood through meticulous analysis of its chemical composition, to identify its various compounds and their average values:

  1. suberin (45%)
  2. lignin (27%)
  3. polysaccharides (12%)
  4. ceroids (6%)
  5. tannins (6%)

It is clear that 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 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.