My cooling duct that came from the factory was a 3D print and was not good. I quickly recreated this to have as a replacement to get me going. It is best if printed in a high temp plastic like HTPLA or PETG since it is located next to the nozzle.
I use 1.2mm top, bottom, and wall thickness and had a 5% fill, which really didn't matter. print with the bottom of the duct on the bed and no supports should be required.