DIY Nano-Air clone.What fabric ?

RSBTR give no indication of permeability and all of the fabric I have in my stash is either too tightly woven and almost windproof or cotton blend or rayon or too heavy to be worthwhile. I have assumed that I need 2 layers of 70CFM to get the needed 35 to 40 CFM needed. Given availability I would probably be using PolarTec Alpha from Mill Yardage. A shame about the Rayon too as my beloved wife has some rally funky patterns in her stash and I like bold bright colours in the depths of a cold winter. That said about weight is 55GSM too heavy to contemplate if the porosity was OK?

Also if the Nanolite has a much higher permeability why is this?

Would this work with Alpha by using something like PowerDry as the liner fabric?

What weight of Alpha? Mill Yardage have both 90GSM and 60GSM at the moment, seeing as how this is for a Canadian winter somewhere off to the North I wonder if warmer is better?

FYI, the polartec alpha #4004 from mill yardage doesn’t require a liner fabric.

Oh? I thought that it was the channel rib 4003 that needed no liner? I didn’t think that would be warm enough but happy to be wrong on that.

Turns out that when on sale it is much cheaper to buy than to DIY

So I just purchased ready made rather than sew my own, it is of the style that Tom advised about above.