Incompressibility: Liquids are practically incompressible, which means their volume does not change significantly under pressure. This property is crucial for brake systems because it ensures a consistent and reliable transmission of force when the brake pedal is applied. Gases, on the other hand, are compressible and would lead to a spongy feeling in the brake pedal, making it difficult to control braking force precisely.

Viscosity: Liquids have viscosity, which means they resist flow. This property helps create a hydraulic seal within the brake system, preventing leaks and maintaining pressure. Gases, having low viscosity, would allow pressure to escape more easily, compromising the effectiveness of the braking system.

Heat Dissipation: During braking, a significant amount of heat is generated due to friction between the brake pads and rotors. Liquids have a higher heat capacity than gases, meaning they can absorb and dissipate heat more efficiently. This property is important to prevent overheating of the brake components and ensure consistent braking performance.

Safety: Liquids are less prone to leakage compared to gases. If a leak occurs in a brake system using gas, it could lead to a sudden loss of brake pressure, resulting in a potentially dangerous situation. Liquids, being contained within closed hydraulic lines, minimize the risk of such sudden pressure loss.

Ease of Maintenance: Maintaining a liquid-based brake system is generally simpler than a gas-based system. Liquids do not require frequent replacement or replenishment, and any necessary maintenance or repairs can be carried out more easily by trained technicians.

Due to these advantages, liquids, typically brake fluid, are universally used in automotive brake systems for reliable, precise, and safe braking performance.