DOT4 is a type of brake fluid used in hydraulic brake systems, particularly in vehicles. It is designed to withstand high temperatures and has a higher boiling point than its predecessor, DOT3. This makes it suitable for high-performance vehicles and those that experience heavy braking. The main components of DOT4 include glycol ether and borate esters, which help prevent moisture absorption. This characteristic is important because moisture can lower the boiling point of the fluid, leading to brake failure. Regularly checking and replacing DOT4 fluid is essential for maintaining optimal braking performance in vehicles.