Early this year, I ordered small quantities of several of these fabrics to test. I found that air would readily pass through all of them (held them to my mouth and blew), which is not the case with silnylon. The company is pretty honest about the weight, as they post reader comments indicating that the sailcloth listed as under an ounce actually comes to over an ounce per sq yd finished, or close to the 1.3-1.4 oz typical of silnylon. I also ordered ".75" oz silnylon from another kite company, Goodwinds, and found that it also came to about the same weight as silnylon readily available, but was much more "crinkly." So at this point, I am pretty much wedded to the silnylon, although I wish there were something less flammable available. I had some old 1.7 oz (total wt) urethane coated that I got from Northface years ago (yes, they actually sold fabrics), and found it was almost as flammable as the sil. I am still leary of the cuben, altho I respect that everyone makes their own choices.
I have to disagree with Roger a little bit though, as after many hours cloistered in my basement workshop, I later found that the sil I used on my first prototype dome was inferior. Note the comments of Ron Bell on his site and posts on this site. The tent was mostly Epic, so I could readily do the sil floor over, but would rather spend the time on my most current designs. The problem seems to be that by the time I get a tent done, I have come up with a much better design. This process carried to its extreme means that no tents get done as I just keep thinking up new designs before getting started on old ones.
So my current emphasis is on coming up with designs that are simplicity plus to construct. After all, the whole idea is to get outdoors.
My opinion from pressure testing is that the the best sil is from Quest and Warmlite, as well as thru-hiker according to Ron Bell, although their color choices are limited. I cannot tell you if it makes a difference to order firsts or seconds from Quest.
Cheers, Sam Farrington, Chocorua NH