Brake Fluid: What Is It Made Of?

Prestone DOT 4 Synthetic Brake Fluid, 12 fl oz


Brake fluid is an essential component of any vehicle’s braking system. It is a type of hydraulic fluid that is responsible for transmitting force and pressure from the brake pedal to the brake pads or shoes, which in turn slows down or stops the vehicle. But have you ever wondered what brake fluid is made of? In this article, we will explore the different types of brake fluid and their compositions.

Types of Brake Fluid

There are four main types of brake fluid: DOT 3, DOT 4, DOT 5, and DOT 5.1. DOT stands for “Department of Transportation,” which is the organization responsible for setting the specifications for brake fluids in the United States. DOT 3 and DOT 4 are glycol-based fluids, while DOT 5 and DOT 5.1 are silicone-based fluids.

Glycol-Based Brake Fluid

Glycol-based brake fluids are the most common type of brake fluid used in vehicles. They are made up of a mixture of glycols, such as ethylene glycol or diethylene glycol, and other additives. These fluids are hygroscopic, which means they absorb moisture over time. This can lead to a decrease in boiling point and a reduction in the fluid’s effectiveness. It is recommended that glycol-based brake fluids be changed every two years.

Silicone-Based Brake Fluid

Silicone-based brake fluids, on the other hand, do not absorb moisture. They are more stable at higher temperatures and have a higher boiling point than glycol-based fluids. However, they are not compatible with most brake systems and should only be used in vehicles that specifically call for them.

Composition of Brake Fluid

Regardless of the type of brake fluid, they all have a similar composition. In addition to the base fluid, brake fluids also contain additives, such as corrosion inhibitors, anti-wear agents, and antioxidants. These additives help to protect the brake system from corrosion and wear, and also help to extend the life of the fluid.


In conclusion, brake fluid is an essential component of any vehicle’s braking system. It is made up of a mixture of base fluids and additives, which vary depending on the type of brake fluid. Glycol-based fluids are the most common type used in vehicles, while silicone-based fluids are only used in certain applications. Regardless of the type of brake fluid, it is important to change it regularly to ensure proper function and safety of the vehicle.