Rust prevention sprays protect the car exterior from damages. Undercoating refers to the application of a protective layer to the under layer of your vehicle. The under layer is prone to rust as much as the exteriors and is also very difficult to clean. Some car owners tend to overlook the need for undercoating as they consider it an additional financial burden. However a car is an expensive investment and it is highly recommended to safeguard your investment through the best possible means.