Diesel Exhaust Fluid

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Diesel Exhaust Fluid (DEF) is a pure, odorless, colorless, synthetically manufactured, 32.5% aqueous solution of urea. DEF is used for the aftertreatment of exhaust gases in a Selective Catalyst Reduction (SCR) catalytic converter.

The SCR catalytic converter can be contaminated by low quantities of metals and thus the quality of the DEF fluid is held to closely controlled standards. DEF cannot be substituted by urea used in agriculture or diluted with any other fluid.

DEF is not categorized as a dangerous substance, it is non-flammable and non-toxic, there is no danger in the event of spills. DEF can be stored on board vehicles, despite the limitation that it crystallizes at temperatures below -11°C (12°F).

In Europe, DEF is also known as AdBlue®, the fluid is specified by ISO22241.