Antifreeze is a liquid added to water in car engines to keep it from freezing in winter or boiling over in summer. Pure water freezes at 32°F (0°C), which would be a disaster for a car engine: when water freezes, it expands with tremendous force, enough to crack metal engine parts. Antifreeze lowers the freezing point of water to well below zero, so even in harsh winter weather, the liquid keeps flowing through the engine.

The most common antifreeze is a chemical called ethylene glycol, usually dyed bright green or orange so mechanics can easily spot leaks. When mixed with water in a car's radiator and cooling system, antifreeze also raises the water's boiling point, which prevents the engine from overheating on hot summer days or during hard work like towing a trailer.

You might notice that many household products use “anti” in their names to show what they prevent: antifreeze prevents freezing, antiseptic prevents infection, and antacid prevents acid buildup in your stomach.

Interestingly, some animals like wood frogs produce their own natural antifreeze: special chemicals in their blood let them survive being frozen solid during winter and then thaw out alive in spring.