Blue DEF is a non-toxic solution of 67.5 percent purified water and 32.5 percent ultra pure automotive grade urea. Blue DEF is not a fuel or fuel additive. Instead, when injected into the exhaust stream and passed over a catalyst, helps convert NOx into nitrogen gas and water vapor, two harmless and natural components of the air. is stable, colorless and odorless, and meets ISO Standards 22241 for purity and composition and is an American Petroleum Institute (API) certified diesel exhaust fluid. These are the highest quality and safety standards in place to ensure optimum SCR performance.