Yes, the 30d stuff. It is completely obvious to me that the pack/stuff sack has almost no tear/puncture resistance, so I've never bothered using it, though I do think it's funny to have a crudely functional 28 gram backpack, heh. Plus the straps were a bit too short for comfort, of course. The actual idea was to have a stuff sack that could double as a small day trip day pack with only a 10gm penalty for the straps, it would work for that I guess. I wouldn't put more than about 5 pounds in a silnylon pack/sack judging from the feel of this little test pack.
If the stresses are distributed enough on the strap connection points I guess maybe it could go to 10 pounds, but that would be as much as I'd expect it to support without failing somewhere at some point in the near future. But the first stumble into a twig or branch or rock would put a hole in it, especially with internal weight/volume pushing out against the surface to make it taut.
But for an ultralight day pack, I have to admit I always chuckle when I see the weights listed for the rei light one people here like, for about 14 grams more I could make this type of pack be durable enough for light day hiking with long enough straps to be comfortable, and about 2x capacity, give or take. At 2oz I think I could have a pocket on it too, not sure.
To me, all you have to do is watch Joe V's progression on materials, he doesn't use silnylon for anything anymore, I believe anyway, and on the packs, quickly is moving away from straight cuben to the hybrid, which is the strength / waterproofness of cuben with the abrasion resistance of 40d polyester. I guess the dimension polyant wx21 and 07 materials are similar ideas, except a bit heavier due to thicker nylons in the sandwich. But the tx07 seems to have essentially no abrasion resistance at all, fun for an experiment though.
I really wish I could find the 70d 1.9 oz silnylon though in normal colors, ie not lime, red, or blackl. That is I think heavy enough to actually work. But that's I guess parachute material, and earth tones probably aren't that big in the parachute world, heh.
The abrasion that concerns me most with using cord for compression straps is the cord against the material, all the force that would be held by a 1/2 or 3/4 inch surface of webbing is instead placed onto a roughly .5 mm contact area of one side of the 2mm cord. I know something put holes into the material of the tx-07 dimension polyant I used for the pack body after only about 60 minutes of hiking with it.
If I get around to it I'll post some pics of using cord for straps and compression, nothing particularly original in it but pictures do show it better.
I've also wondered about the abrasion of the cord vs lineloc3, I'd guess 2mm cord will abrade, 3mm cord probably not so much. But the good thing with cord, unlike straps, is that it's tied on, not sewn on, so replacing it in the field is easy using some spare cord you would be carrying anyway.