A spoiler is a structure built into the body of car, usually on the back of the car behind the rear window, which is designed to reduce wind resistance by disrupting inefficient airflow. The faster a car drives, the more it must cut through the wind, and the more air resistance the car experiences. Generally the more surface area that is exposed to the wind, the more drag the car will generate, meaning the added surface area of the spoiler adds some drag. On the other hand, a spoiler diffuses airflow in such a way that drag is reduced on other areas of the car, resulting in an overall reduction in drag and increase in aerodynamic efficiency.