What Is DEF Fluid Made of? Diesel Exhaust Fluid (DEF) which is composed of 32.5 percent urea and 67.5 percent deionized water. For those who like trivia, urea is considered to be the first organic compound to be synthesized from inorganic chemicals.

What is DEF made up of?

It's called Diesel Exhaust Fluid (DEF). This additive is also called aqueous urea solution 32% or AUS 32. It's made from 32.5% urea and 67.5% de-ionized water. Read on to find out everything you need to know about the DEF in your DEF system.

Is DEF fluid made from pig urine?

Urea is an organic compound produced when a body metabolizes protein. (And yes, we expel it as urine.) But despite DEF earning the nickname “pig urine,” Diesel Exhaust Fluid is actually made of commercial-grade urea—synthetic ammonia and carbon.