Cooling fans are used to control the temperature of motors and ESC in RC cars. This improves the lap-times and consistency in Stock and Modified Racing.
But the most fans are installed in a rather not ideal place. They either to close or not close enough to the motor. If the Fan is installed to close it is affected by the strong magnet of the rotor. If installed to far away the Fan only blows some air directly to the motor. In either case a lot of cooling performance is left on the table.
Fan Shrouds are used to counter these issues. They will direct the Airflow to the motor while keeping a safe distance to the rotor's magnetic field.