Prestone Command diesel exhaust fluid (DEF) is a colorless, odorless, nontoxic and nonflammable liquid solution consisting of 67.5% demineralized water and 32.5% high-quality automotive-grade urea. It meets all API and ISO 2224-1 manufacturing specifications. DEF will corrode certain metals, such as aluminum, copper and brass, so it must be used and stored with dispensing equipment and tanks that are made of stainless steel or high-density polypropylene. It is available in 1- and 2.5-gallon containers, as well as 55-gallon drums and 330-gallon totes.