Rust Bullet Automotive and Rust Bullet ProPLUS are both are designed to protect metal surfaces from corrosion, but they differ in formulation and specific use cases. Automotive is our original formula that received two United States patents for rust prevention and corrosion control and will provide the highest level of protection. ProPLUS is a slightly thinner version of Automotive that maintains a lot of the same properties while achieving Low VOC content, making it compliant in all 50 states. ProPLUS is designed as a budget-friendly option without compromising on rust-inhibitive qualities. The thinner formula of ProPLUS will typically require additional coats as opposed to Automotive to achieve the same mil coverage for protection.