Clean Ayr guarantees its customers American Petroleum Institute (API) certified diesel exhaust fluid (DEF). Our DEF is handled in accordance with the International Standards Organization (ISO) compliance regulation for DEF; ISO 22241. Clean Ayr buys and delivers the best DEF. Our DEF is tested and certified as 32.5% urea and 67.5% deionized water according to the United States National ASTM D7821-12 (21018) “Standardized Test Method for Field Test Determination of Urea Concentration in Diesel Exhaust Fluid.” We stand behind our products and give our customers the best DEF possible.