When automobiles move at a fast speed, the resistance offered by the air becomes very large. This results in a loss of power and reduces performance as well as efficiency. It is therefore essential to reduce the resistance due to air by designing the automobile's exterior appropriately.
Cars that have a closed top allow the air to flow past it a relatively easy way. On the other hand, convertibles due to their design create a large air drag. One way to reduce this is by placing a glass shield behind the headrest. The glass shield reduces air resistance but while doing so it results in the air within the cabin getting trapped and slowing down its speed.
When the fast moving air that flows over the driver's head meets the slow moving air in the cabin, vortexes are created. Vortexes are a form of air turbulence that make the air rotate and spin. The are similar to tornadoes, only turned 90 degrees to act in the horizontal direction. These vortexes push air from the back of the convertible towards the front. This results in the hair of people in the car blowing forward instead of backwards.