Cork oak (Quercus suber) with sections of cork removed—Eric Carle/Shostal Associates
Outer bark of the evergreen cork oak (Quercus suber), native to the Mediterranean. In its broad sense, cork consists of the irregularly shaped, thin-walled, wax-coated cells that make up the peeling bark of many trees, but commercially only cork-oak bark is called cork. Cork is obtained from the new outer sheath of bark that forms after the original rough outer bark has been removed. This outer sheath can be stripped repeatedly without hurting the tree. Cork is unique because it is made of air-filled, watertight cells that are a remarkably effective insulating medium. The air pockets make cork very light in weight. Though specialized plastics and other artificial substances have replaced cork in some of its former uses, it has retained its traditional importance as a stopper for bottles of wine and other alcoholic beverages.