Diesel exhaust fluid (DEF) is one of the key elements of the selective catalytic reduction process used by diesel engine builders to meet EPA 2010 regulations. BlueDEF is a nontoxic solution of 67.5 percent purified water and 32.5 percent ultra pure automotive grade urea. BlueDEF is not a fuel or fuel additive. Instead, when injected into the exhaust stream and passed over a catalyst, BlueDEF helps convert NOx into nitrogen gas and water vapor-two harmless and natural components of the air we breathe.