Cork is a plant substance called phellem and covering the trunk of a tree called cork. Each year going "born" rings trunk inside out, thus forming the shell. The cork is made for different areas, Portugal being the largest producer, followed by Spain and Italy in third.

As late as the mid-17th century, French vintners did not use cork stoppers, using oil-soaked rags stuffed into the necks of bottles instead. Wine corks can be made of either a single piece of cork, or composed of particles, as in champagne corks; corks made of granular particles are called "agglomerated corks".

The features of the Cork are:

World production of cork is about 340,000 tons, of which Portugal produces 61%, Spain 30% and Italy 6%.

Lightness: it is because 88% of their volume is air, which results in a low density.

Waterproof: the diffusion of liquids and gases through the cork is very difficult, thanks to the suberin and ceroid present in the walls of their cells, cork is substantially impermeable to liquids and gases. Its resistance to moisture allows you to grow old without damage, hence several wine amphorae found in the sea conservasen cork closure in perfect condition.

High calorific value: the ability to generate heat cork is equivalent to the charcoal, about 7,000 Kcal / kg.

Easily manageable: artificially modified the water content of cork, by boiling for example, industrial processes are given, mainly cutting, turning softer and elastic.

Low water content: moisture equilibrium with the environment cork, after removal of scrapes, no more than 9% of their weight, typically 6%. This low humidity makes impossible the growth of microorganisms.

Thermal insulation: natural cork function is to protect the living parts of the tree that generates it. Its honeycomb structure (preventing circulate air), low water content and lack of conductivity of compounds enables it to perform its role effectively insulated. Presents a heat aging resistance thirty times that of the concrete.