Rust Check is a two product process'. Rust Check is a light liquid oil-based product with active corrosion inhibitors. Its main function is to penetrate into crevices, displace existing moisture, and then keep moisture from re-entering. Without moisture, corrosion cannot occur. Coat & Protect is a thicker version of Rust Check, with the same active ingredients. Its thickness gives it good wash and wear resistance. The main function of Coat & Protect is to protect exposed areas of the undercarriage. Unlike traditional undercoating, Coat & Protect is non-drying, so it won't crack or peel. Coat & Protect also is an excellent heavy duty lubricant.