Cardboard seems to work better than the duct I made. The other thing that seems to work pretty well is that compressed cardboard stuff you get in the 'projects' section of lowes / home depot lumber area. It's easy to work with and you can quickly cut out forms that would enclose all the cards.
Looking for an efficient air duct design, any luck on a redesign of yours or maybe you could point me to someone?
You'll want to hop on discord and speak with @Conlaeb#4993 -- He has a number of designs