Helps to cool an object quicker at the end of a print (which shortens the wait time for the object to be released from the bed) by providing a more directed airflow across the surface of the glass and around the base of the object. The cross-sectional area of the duct opening is kept as close to that of the circular fan inlet to maximise airflow. If the under-bed wadding is removed during cool-down then some of the air can be directed below the glass, thus improving the cooling effect further.Print it. Fit it to the inside of the inside of the rear buttress where the fan usually goes, with the fan and fan guard on the outside. The STL is rendered to fit a standard Mendel90. The gap between the front edge of the duct and main dibond gantry is intentional - I have LED strips running around the gantry opening to illuminate my print area. You can adjust the fan duct opening dimensions and position in the SCAD. Just try to keep the cross-sectional areas of the fan intake and duct openings roughly equal to avoid throttling the airflow.