Also known as conversion coating, chem film is a surface coating for aluminum. The color can vary from a dark golden brown to a light yellow tint. Chem film produces a conductive protective coating without any dimensional change. Aluminum components should be chem filmed prior to assembly, to avoid leaving bare, unprotected areas where the parts are joined or riveted. There are two types of chem film: Class 1A and Class III. Class 1A is used as a corrosion preventative film. It can also be used to improve the adhesion of a paint finish. Class III is used for protection against corrosion where low electrical resistance is required. Thickness for chem film is less than .000001”.