Cork is the outer bark of the cork oak tree, Quercus Suber, which grows mainly in the Mediterranean region. The bark is a vegetal tissue composed of an agglomeration of cells filled with a gaseous mixture similar to air and lined with alternating layers of cellulose and suberin. Cork's elasticity, combined with its near-impermeability, makes it the perfect material for making bottle stoppers, floor tiles, insulation sheets, bulletin boards and other similar products. Because of its remarkable qualities, cork is used in high-tech applications including car engines, dam mechanisms and airport runways. The aeronautics has used cork as a thermal insulator in space shuttles.