I looked for something like this but didn't find any 3 inch flexible duct versions that also didn't use lots of filament, so I designed this flexible duct adapter for my Antminer S9 so I could easily channel hot exhaust outside for the summer. It will mount on any 120mm computer fan so could be used for many other purposes than bitcoin miner exhaust work.
I made this to be used with an inline booster fan I designed here: https://www.thingiverse.com/thing:3630807
Will add more photos later.
Printed at 0.2mm layer height, using Amazon Basics PETG
Custom Large Format FDM Printer
Amazon Basics PETG
As long as your perimeters don't have gaps, this will work well at any infill setting...