Clever Fluid
Brake fluid is a non compressible fluid that is used to transmit pressure from the brake lever to the brake pads pushing against the disc rotors. Simple enough you might think but actually it is pretty clever stuff.
Brake fluid is actually called upon to do many different things.
It has to transmit pressure and do so without volumetric variation.
It also has to act as a lubricant as the circuit includes a number of moving parts.
It must not be corrosive to other system components.
It must have a very low freezing point (less than -40 deg C)
It must have a very high boiling point due to the amount of heat introduced by friction.