Ani-freeze does contain Ethylene Glycol, but may also contain Methanol. It lowers the freezing point of the coolant. The stronger the mixture up to a certain level, the lower the freezing point . when it does start to freeze it forms solid water ice, so the coolent gets stronger and so lowers the freezing point of the mixture, so only a small amount os slush forms. It also contains antl-corrosion treatment for the aluminium and steel engine components, so it must still be used in summer, and replaced from time to time particuarly if new components are fitted.