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Cork Properties

Cork’s particular structure provides it with a number of physical properties which are:

Lightness. Cork is made of a compact structure with approximately 36 million cells per cm3 filled with nitrogen and oxygen which make up 89.7% of its matter. The remaining cell volume that is empty is almost 90% giving rise to its floating ability as shown by its long history of use in the production of buoys and fishing nets.

Elasticity. Due to the membrane flexibility the cells function as microscopic air cushions which regain their shape once compressed. This property, called elastic return, characterizes a ‘good’ cork stopper and results in its sealing ability. Its elasticity allows it to take the form of the bottle neck, regardless of its shape, even irregular, with an elastic return strength that keeps it firmly pressed against the glass walls.

Impermeability. Its impermeability is due not only to the counter-pressure exerted by the gas in the cells but also due to the presence of a high proportion of fatty substances (suberin, cerin...) in the cork membranes.

Insulating. Suberin, infusible and insoluble, whether in water, alcohol, chloroform or acids, provides cork with impermeable properties which allows cells to fill-up with air and take on a strong insulating and protective ability.

Inert. As it is a dead tissue1 it can be considered an inert substance, without odour or taste. It therefore has a strong hygienic value, a characteristic much appreciated by the bottle stopper industry.

Adherence. Its adherence to glass is first a consequence of the expansion force of an elastic material against a rigid wall but it is also due, and this is an important point, to the many cells that when cut simulate microscopic vacuum pads; these adhesive properties are further enhanced by the presence of resinous substances in the cork.

Durability. Cork is a very resistant substance of strong durability with a remarkable capacity to conserve or retain the initial unalterable properties. We can consider it an unalterable and imperishable material.

1 At the moment of transformation the cork is boiled for 75 minutes to remove all organisms, extract contaminants and make the sheets softer and flexible.