More information about cork 

Cork is the bark of an oak tree known botanically as QUERCUS SUBER. The tree is an evergreen that grows only in areas bordering the Mediterranean. Portugal represents approximately 50% of the world’s cork output, Spain accounts for 25% and the remainder comes from Algeria, France, Morocco, Italy and Tunisia.

As early as 2500 BC, cork was being used for fishing floats in ancient Egypt. The ancient Greeks also used cork to make fishing buoys, sandals and stoppers for vessels containing wine and olive oil.
The conqueror Alexander the Great is reported to have been one of the many historic figures to have used cork. It is said that a piece of cork once saved him from drowning when crossing a turbulent river.

The Romans used cork in the construction of house roofs, beehives, ships and women's shoes.
In the 1600s, a French monk called Dom Pérignon took a giant step towards the modern, widespread use of cork as a stopper for bottles of wine.
In the 20th century, cork was the only organic substance to travel to Mars when it was used for thermal insulation in the Viking space probes.

A natural “green” product

In these times of increased concern for the environment, cork remains the only tree which can regenerate itself after each harvest. The cork bark is stripped off two-thirds of the tree. The first harvest of cork is not stripped until the tree is approximately 20 years old. A thin layer of protective inner bark gives the cork oak its unique ability to survive and regenerate itself after the debarking process. Stripping the bark requires great skill, as the inner bark must not be damaged. A specially designed hatchet is used for the stripping process.

The first bark taken from a tree is called virgin bark. It has a very irregular exterior surface and is grayish in color. This bark is suitable for grinding into various minute sizes ideal for cork insulation and composition cork. Interestingly, it has also become a very popular material for the manufacture of decorative items.

After the first harvest of cork, the bark is stripped from the tree once every nine years, until the cork oak is about 150 years old. The tree is then replaced by a much younger one. The bark which grows after the virgin bark has been stripped is called refugo bark. It looks entirely different, having a much smoother surface, which is brown in color. The first crop of refugo is used mostly for grinding. Subsequent strippings yield better quality cork that has fewer and more tightly closed pores (grains). Most of the cork from these subsequent harvests is used for the production of cork stoppers or other items requiring cork with a finer appearance.

After being stripped, the bark is left in the forest for some days to dry and, possibly, to be inspected by potential buyers. Purchasing cork bark is not an easy task as the quality not only varies from forest to forest, but also from tree to tree. Even the same tree may produce cork of varying degrees of quality depending on its exposure to sunlight.

Once in the factory area, the refugo bark is boiled to make it easier to remove the woody outer layer and to make the bark more elastic so that it can be flatten it out more easily. The bark is then sorted into various thicknesses which are, in turn, sorted into different qualities. These different qualities determine the sale price and/or the suitability of the cork for different manufacturing uses.

Cork is a natural product with remarkable and unique qualities that are unmatched by any other natural material. One cubic inch of cork is composed of no less than 200 million tightly enclosed air cells, each measuring l/1000" in diameter. Each minute cell is 14-sided, which virtually eliminates any empty space between the cells.
This quality is what gives cork its remarkable elasticity and ability to regain its original shape after being compressed.