A polyurethane coating is a polyurethane layer applied to the surface of a substrate for the purpose of protecting it. These coatings help protect substrates from various types of defects such as corrosion, weathering, abrasion and other deteriorating processes. Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives.