Hydraulic or pneumatic:

Car brakes can be both a hydraulic( liquid) or pneumatic ( air). Normal family cars usually uses hydraulic system because its cheaper and normal cars does not require a lot of force to slow down, also it needs to be much quieter in a car since some drives for long distances. Air brakes are used in larger vehicles because it requires much more force than the hydraulic brakes are able to produce, air brakes generates much larger pressure than hydraulic brakes if the brake size are the same. However Air brakes are more difficult to maintain and won't last as long.