Special types of oil like mineral oil are used in hydraulic brakes. 

Nature of such oil listed below make them suitable for their use in hydraulic brakes:

1. Non-Hygroscopic: Oil used in hydraulic brakes don't absorb moisture from the air. This property helps maintain consistent brake performance, as moisture can lower the boiling point of brake fluid and lead to brake failure.
2. Compatibility with Seals: Such oil is less aggressive on rubber seals compared to other fluids. This compatibility extends the life of the seals, reducing the risk of leaks and maintaining effective braking