This guide provides test procedures for assessing the susceptibility of organic coatings on metal substrates to filamentous corrosion. Filamentous corrosion typically occurs when the coating breaks and the relative humidity is between 70% and 95%. The guide includes three procedures for determining whether coatings will produce filamentous corrosion under these conditions. The guide clarifies the scope and conditions of testing, ensures Reliability of evaluation results and reminds users to consider relevant safety and health practices before application.