To obtain the best print quality, especially when your model has overhangs, you need to cool the printed material as soon as possible after it leaves the heated nozzle. While the standard Prusa duct is adequate for most jobs, gains can be had by replacing it.

This air duct assembly by teookie on Prusa’s Printables.com was designed using CFD analysis to predict air flow characteristics and is designed to replace the standard Prusa ducting. Instead of the air flow coming from one just the front of the standard duct, the replacement part has the flow split into two and directed from either side of the print area. When printed in a high temperature filament such as PETG or ABS it is able to withstand the heat of the hotend.