Brake fluid serves as a force distribution and transfer medium where a non-compressible fluid transmits hydraulic pressure from the master cylinder to the brake calipers.

The effectiveness of brake fluid depends on its ability to maintain non-compressibility within the specified parameters of its class or specification. Brake fluids are subjected to rapidly increasing temperatures, often exceeding the boiling point of water (100°C). Excessive moisture absorption can lower the fluid’s boiling point, leading to the formation of air bubbles—air being compressible. Similarly, premature boiling of inadequately performing brake fluid can lead to vaporization, generating air bubbles that can rapidly degrade the performance the braking system. To accommodate for absorbed moisture, wet boiling point limits are specified.