In automobiles, fade, or brake fade is the reduction in stopping power caused by a buildup of heat in the braking surfaces (and in the case of drum brakes the change in dimension of components in response to heat; the curvature of the brake shoes then failing to match the curvature of the brake drum) . It occurs most often during high performance driving or when going down a long, steep hill. Owing to their configuration this is more prevalent in drum brakes. Disk brakes are much more resistant to brake fade and have come to be a standard feature in front brakes for most vehicles, although the brake rotors can become warped due to excessive heating. Fade can also be caused by the brake fluid boiling, gas is released and since gas is compressible you get a spongy pedal. Obviously it's worse when there are contaminents in the fluid such as water which some types of brake fluids are prone to absorbing.
Brake fade and rotor warping can be reduced through proper braking technique; When running down a long downgrade that would require braking simply select a lower gear (for automatic transmissions this may necessitate a brief application of the throttle after selecting the gear). Also, periodic, rather than continuous application of the brakes will allow them to cool between applications. Continuous light application of the brakes can be particularly destructive in both wear and adding heat to the brake system.