There are three main types of brake fluid: DOT 3, DOT 4, and DOT 5.
DOT 3 and 4 are glycol-based brake fluids, and the main difference between them is the boiling point: DOT 4 boils at a higher temperature, which can be beneficial if your brakes see very heavy use, or if you participate in motorsports. Of course, you should check your owner’s manual first to make sure DOT 4 can be used in your vehicle.
DOT 5 fluid is silicone-based: It doesn’t absorb moisture like DOT 3 and 4 fluids do, and it has a higher boiling point. However, DOT 5 fluid should never be added to vehicles that specify DOT 3 or 4 fluid, as brake system damage can occur.