Blue Def is a stable, colorless, non-flammable, non-toxic and is classified as minimum risk for transportation. Conforms to the ISO-22241-1 specification for DEF, is API registered and meets or exceeds OEM specifications. Blue Def is a mixture of 32.5% high purity synthetic urea and 67.5% deionized water that is used is Selective Catalytic Reduction (SCR) systems on diesel engines. DEF is the primary ingredient used to help convert NOx to harmless nitrogen and water.