The bark of the cork oak tree has a unique honeycomb structure composed of tiny cells filled entirely with air. The properties of cork derive naturally from the structure and chemical composition of the extremely strong, flexible membranes that are waterproof and airtight.
It should be remembered that each cubic centimetre of cork's structure contains between 30 and 40 million cells.
Because about 89% of the tissue consists of gaseous matter, the density of cork is extremely low, in the order of 0.12 to 0.20.
Some of cork's most unique and useful properties are:
Cork is light and will float on water. For many thousands of years, this has been its most evident and most celebrated characteristic. In antiquity cork was used in fishing equipment.
Elasticity and Resiliency:
The cellular membranes are very flexible, making the cork both compressible and elastic. These characteristics, in alliance with others, largely explain how cork has become indispensable for stoppers.
This capacity means that the cork can be fitted perfectly against the walls of the bottleneck. When cork is subjected to strong pressure the gas in the cells is compressed and reduces considerably in volume. When released from pressure cork immediately recovers its original volume.
The presence of suberin (a complex mixture of fatty acids and heavy organic alcohol) renders cork impermeable to both liquids and gases. As a result it does not rot, and may therefore be considered one of the best seals available.
Insulation & fire retardant qualities:
Cork has one of the best insulating capacities, thermal and acoustical, of all natural substances. This is due to the fact that the gaseous elements are sealed in tiny, impermeable compartments, insulated one from the other by a moisture resistant material.
Cork is a natural fire retardant as it does not spread flames and does not release toxic gases during combustion.
Resistance to wear:
Cork is also remarkable resistant to wear and has a high friction coefficient. Thanks to the honeycomb structure of the suberose surface it is less affected by impact and friction that other hard surfaces.
Cork does not absorb dust and consequently does not cause allergies nor pose a risk to asthma sufferers. It is constitutionally inalterable and so its efficiency is guaranteed.