A protective covering is an item or material that is used to protect something from damage or wear. A LINER is a thin layer of material that is placed inside something to provide protection. A SHEATH is a cover or casing that is used to protect something from damage or wear. COATED refers to a material that has been covered with a thin layer of another material, such as paint or ENAMEL. ENAMEL is a type of coating that is made up of a combination of glass and other materials, and is used to provide a glossy finish and protection.