The DOT specification is an indication of how high that particular brake fluids’ boiling point is. DOT 3 has a lower boiling point than a DOT 4 brake fluid. This does not mean that DOT 4 is automatically better though as it is entirely dependent on what your car’s braking system specifies. Those with higher boiling points are well suited for high-performance racing cars, as their braking systems tend to generate enormous amounts of heat. Then you also have to consider that the DOT 3 brake fluid tends to absorb less moisture over time, so that makes it the lower maintenance and economical choice.