Packs would probably attract as much controversy as alcohol stoves if they were easier to make and more folks did it. So you will probably get opinions going all over the place.
For what it's worth here are my prejudices:
a) 1.3 oz silnylon works for me on everything but packs that are to be subjected to public transportation, including hitching and lots of butt-sliding over granite –IOW, for the AT or other long trail use. For that, I think Dyneema grid-stop makes sense. With that said, I have UL packs that have survived the AT – at the cost of a certain amount of anxiety.
b) Flat, wide packs keep the load closer to the back and better balanced than bulging bags like the Breeze. Matching stuff sacks provide structure and superior load control.
c) For long trails, good load control means reducing the size of the bag as the food load shrinks, so some form of compression is a good idea. For short trips, compression is irrevelant, and the bag can be as clean as possible. Side compression keeps a flat bag flat while front compression tends to give it an undesirable barrel shape.
d) If you use detachable shoulder straps, you can move them from bag to bag. Shoulder straps are a pain to make, and I avoid doing it when I can. I have a good contoured design and several straps made on that design, so I reuse them – pull them off one pack and put them on whichever pack I plan to use next.
You can turn out a light weight pack bag in an afternoon or two. That means you can have several bags sized for the season and the load and not have to worry with compression issues. Just move your strap set from pack to pack. Shoulder straps can be attached with 8" strips of 4" Velcro. At a minimum of 5 pounds of strength per square inch, one strip per strap will hold 160 pounds. That ought to do it. Make the strips on the pack longer to provide torso length adjustment. For reasons that escape me, Velcro narrower than 4" does not work as well even when using one per strap — whereas, you can put both straps on a single 4" strip. Go figure.
e) Large sleeve pockets on the sides of either mesh or nylon, but certainly with mesh bottoms, can hold water and fuel and a leak will not get in the pack.
f) As mentioned earlier in this thread, roll-down tops let you vary the load and compress the pack from the top for load control. They are also weather resistant (as a final protection, not as the first line of protection), and they work better with the wide, shallow pack recommended in b). Contrast that with the drawstring top of the Breeze which tends to result in a cylindrical top. In practice, letting the top go cylindrical does not hurt the balance much, but the drawstring, while a little lighter, does not let you vary the load much.
g) If you make your own packs, you can experiment with unusual ideas. But start simple. My favorite is to go without a hip belt. Almost everyone who starts out to make a MYOG pack tries to incorporate a hip belt, but they rarely, if ever, work as intended. As Ryan Jordan demonstrated in an article on pack design here at BPL ("Frameless Backpacks: an Engineering Analysis"), packs without supporting frame members such as stays will compress between the hip belt and shoulder straps, eliminating the support the hip belt is supposed to provide. I don't use hip belts for loads under 35 pounds or so, and find my walking is easier. Hip belts restrict full body movement, reduce your stride length, put pressure on critical muscles, and generally get in the way of walking.
h) Beware foofawraw – anything you add to a simple bag means more weight, and it adds up fast. A 5 ounce concept can quickly double in weight with extra straps, reinforcements, pockets, etc. Also beware mixing incompatible materials – especially heavy or stiff webbing or reinforcement material on UL nylon. The result will be a dog's breakfast. Be aware that UL packs have little inherent structure and heavy or stiff components will distort them, strain the fabric and cause failure.
