Unique Cell Structure & Low Density (Light Weight)
The bark of the cork oak tree has a unique honeycomb structure composed of tiny cells. Each cell has the form of a 14-sided polyhedron and the inner cell space is entirely filled with an air-like gaseous mixture. The properties of cork derive naturally from the structure and chemical composition of its extremely strong, flexible cell membranes, which are waterproof and airtight.
Because about 89% of the tissue of the bark consists of gaseous matter, the density of cork is extremely low, in the order of 0.12 to 0.20, a fact that bears witness to the huge disproportion between the volume and the weight of the material. This means that cork is light weight and floats on water. For many thousands of years, this has been its most evident and most celebrated characteristic. Since ancient times, cork has been used in fishing equipment. Cork's low density makes it a suitable material for fishing floats and buoys, as well as handles for fishing rods (as an alternative to neoprene).
The presence of suberin (a complex mixture of fatty acids and heavy organic alcohol) renders cork impermeable to both liquids and gases. Thus, it does not rot, making it one of the best seals available. Furthermore, cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle stoppers, especially for wine bottles. Moreover, the cell membranes of cork are highly flexible, making it both compressible and elastic. This means it returns to its original shape after being subjected to pressure. This and other characteristics explain why cork has become an indispensable material for making bottle stoppers. Cork stoppers represent about 60% of all cork based production.
Insulation and Fire Retardant Qualities
The value of cork is further enhanced by its low conductivity of heat, sound and vibration. This is because the gaseous elements it contains are sealed in tiny, impermeable compartments in a bubble-form cellular structure, insulated from each other by a moisture-resistant material. This endows cork with one of the best insulating capacities, both thermal and acoustic, of any natural substance.
Cork is easily compressed due to the cellular structure of the material which allows for expansion after compression to its original form. It neither spreads flames nor releases toxic gases during combustion.
Resistance to Wear
Cork is remarkably resistant to wear and has a high friction coefficient. Thanks to its honeycomb structure, it is less affected by impact or friction than other hard surfaces.
Cork does not absorb dust, it helps protect against allergies and does not pose a risk to asthma sufferers. It also has an unchangeable constitution that guarantees efficiency. Corks impermeability also allows for little to no water & gases absorption.
Low Thermal Conductivity
Granules of cork can also be mixed into concrete. The composites made by mixing cork granules and cement have lower thermal conductivity, lower density and good energy absorption. Some of the property ranges of the composites are density (400–1500 kg/m³), compressive strength (1–26 MPa) and flexural strength (0.5–4.0 MPa).
Use in wine bottling