Brake fluids are composed of 3 main components.

SOLVENT 60 to 90%

Polyglycols have a high viscosity, therefore it is essential to dilute them with a product with low viscosity (polyglycol ethers). Polyglycols ethers play the role of solvent in the fluid. They have to dissolve polyglycols and all other components in such a way to get a single-phased fluid offering satisfactory lubrication under all temperatures.

LUBRICANT BASIS 5 to 30%

Polyglycols are used as lubricants in proportion of up to 30% in brake fluids. They are acquired by reacting alkylene oxides (ethylene and propylene) with bifunctional components like diols or water.

ADDITIVES 2 to 5%

Brake fluids regularly contain up to 5% of additives. Corrosion inhibitors are added to protect the brake system metals from corrosion and antioxidants are necessary to decrease the oxidative decomposition of glycol ethers polyglycols and to delay the formation of acidic decomposition products and resins.
These two inhibitors' categories are important to ensure a long-term and satisfactory brake fluid service life.