There's actually two, one guy used Vinyl Vehicle Wrap material (I Didn't have any handy and it's somewhat expensive unless you have some laying around, depending on the brand it may or may not be heat shrinkable too) to wrap around the original parts and the other guy used ShopVac hose. The ShopVac hose is pretty good, but due to the sizes available, it'll only fit INSIDE of the existing vents.
I was aiming for cheap (11.99 shipped on Amazon with Prime) and functional (did not make any changes to diameter, and it's strong enough to support itself).
BTW, I'm one of your YouTube subscribers, some good info you've shared on there!
