Originally Posted by Youngblood
With the hammock material being a vapor barrier you aren't going to be passing moisture through your underquilt so you don't need it to be breathable, except to get it to loft and possibly remove any moisture that might find its way in. Heck, with a hammock that is a vapor barrier you can't realize the advantages of breathable underside insulation in warmish conditions anyway. Sounds like what you did is a win-win situation as you don't use it with a hammock that has breathable insulation. If you ever want to use that underquilt with a hammock that has breathable insulation then the cuben bottom will likely be a problem.
Also, that UQ could have a 100% waterproof shell ( totally surrounding the down, not just thre bottom layer), with only allowances ( some how) for compressing into a stuff sack and drying out if it manages to gets wet. IOW, the down could be treated like the down in the Exped Downmat. It could be pretty much impervious to fog, rain or condensation of perspiration.
In fact, a quilt made in this fashion would be it's own VB, not needing the VB effect of the cuben hammock fabric.
Of course, getting the air into it for lofting up, and getting the air back out for compression into the stuff sack, would be factors to be overcome. Also, if it did get wet despite all of this, you would have to have a means of exposing the down to dry air. So probably, we are realistically only going to be able to mostly cover with a WP barrier. A completely separate, removable shell comes to mind, but that is added weight. But so is a sock and such.
And folks might not like the feel of it, especially if it is warm weather. But, if you are using a VB hammock anyway?