A rear diffuser is an automotive aerodynamic modification typically found mounted on the vehicle’s underbody located at the rear of the vehicle, underneath the rear bumper. As a vehicle is in motion, air flowing in the underbody is typically at high-speed and has low-pressure. The design and purpose of a diffuser are to help reduce drag and to create downforce by facilitating the airflow underneath the vehicle’s underbody. A diffuser is used to increase the air volume along its full length, thus creating a void that must be filled by air. This in turn creates a Venturi effect, meaning the air flow is accelerated at the beginning of the diffuser creating a low pressure, thus creating downforce. As the air travels along the full length of the diffuser, the high velocity air is eased back into normal velocity matching the ambient velocity at the rear of the vehicle reducing overall drag. With the addition of vertical “fins” attached to the diffuser, this helps to optimize the diffusers efficiency by ensuring that all air being drawn into the diffuser is from the underbody and isn’t being drawn from the upper body surfaces. A diffuser is best optimized with the addition of a front splitter to help mediate the underbody’s airflow.