Smart coatings are defined in many different ways. One of the best is: “A smart coating is one which is able to sense a change in its environment and respond to that change in a predictable and noticeable manner.” So, to be considered “smart,” a coating must be able to offer something which is over and above the normal function of a typical coating, such as color, protection or waterproofing. Smart coatings can be self-repairing, optically active, bioactive, self-cleaning or respond and react to pollutants.