n The outer bark of Quercus suber, a species of oak native to Mediterranean countries, having density in the range 0.22–0.26 g/cm³. Cork is used as a core material (see  Core (1)) in sandwich structures and, in ground form, as a density-lowering filler in thermoplastic and thermosetting compounds for special applications such as flooring, ablative plastics, insulating compositions, and shoe inner soles.