Cork does indeed grow on trees!  It is a natural product we have harvested without harm to the tree.  Mankind has often taken what nature provides either for granted or assumed it can do better.  Synthetic substitutes have bot been able to reproduce cork with all its complexities.  Any that come close in a particular aspect are becoming increasingly expensive and in many cases will not retain its performance over the years as cork will.

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Its properties include recoverability, sound and heat insulation, the ability to breath and yet to seal.  Moveover, it is just as versatile for the actions that it will not do.  It does not disintegrate under adverse weather conditions.  It does not give off gases.  It does not support combustion.  No parasite lives off it.  In short,, it is basically inert.   It is an unique cellular structure which consists of a vast number of tinu 14 sided cells, each containing a microscopic volume of gas.  The gas is similar to air but without CO2, 50% of the cellmass is composed of this gas.  Furthermore it is non corrosive, has useful flame-retardant properties and will withstand high compression loading.  The cell walls comprise of several membranes forming a strong impermeable and elastic structure to contain the gas (with around 40 million cells per cubic centimetre)