Cork is the outer protective layer of bark of a tree. The cork cells are dead and compactly packed with no intercellular space. Their cell walls are coated with a waxy substance, suberin, which do not allow water and gases to pass through. Therefore, it protects the plant against mechanical injury and also prevents the loss of water by evaporation. Cork is hard and very rigid which can give good insulation. Protective tissues are a special type of tissues which protects other cells and tissues from the external injuries, basically, it works as an external barrier which prevents the external forces.