AbstractCork is a natural cellular material of biological origin with a combination of properties that make it suited for worldwide use as a wine sealant and insulation material. Cork has low density, is buoyant, is not very permeable to fluids, has a low thermal coefficient, exhibits elasticity and deformation without fracturing under compression, and has considerable durability. Such characteristics result from the features of its cellular structure, primarily its cell dimensions and topology, and from the chemical composition of the cell wall. The characteristics of the two main chemical components (suberin and lignin, which represent 53% and 26%, respectively, of the cell wall) have been analyzed. The limits of natural variation and their impacts on cork properties are discussed and used to define the material as “cork”.