According to its Safety Data Sheet it contains 2-Butoxyethanol dissolved in Ethylene Glycol. 2-Butoxyethanol is a butyl ether of Ethylene Glycol. 2-Butoxyethanol is often used as a surfactant, which may explain how it might prevent deposits. It's also used in paints and household cleaners. In fact, it is apparantly the main ingredient in many household cleaners. Also approved by the Food and Drug Administration as a food additive. Ethylene Glycol on the other hand can be toxic. Ethylene Glycol is used in automobile antifreeze which might explain how it prevents DEF from crystallization and freezing. Dosing looks to be about 1-2 ounces of NüDef into a 2.5 gallon jug of DEF.