- BlueDEF Purity Guarantee is our assurance the DEF your are purchasing has been tested to meet or exceed the strictest OEM standards - America's #1 brand of Diesel Exhaust Fluid - Conforms to the ISO-22241-1 specification for DEF, and is an American Petroleum Institute (API) certified diesel exhaust fluid - Compatible with all diesel SCR systems - Non-flammable formula makes handling safe and easy