Thanks, that's exactly the sort of info I need. I've used 1.9oz (70d) ripstop in two packs, for the front and side panels, but neither pack has seen a lot of use.

I hadn't seen the Vargo pack before. As someone who started with an external frame pack, I know they have some advantages (and some disadvantages, too.) I always thought that the evolution of the external frame was incomplete, but of course internal frame packs took over the market.

In the old days, manufacturers made a big deal about the strength of the frame, usually using 1" diameter aluminum tubing, although a few used 3/4" (notably Trailwise and Jansport). I think 1/2" aluminum would be strong enough, especially with the lighter loads people carry now. Titanium is lighter and stronger, but expensive.

I read a few reviews of the Vargo pack, and people seem to love them, but all mention the same things they'd like changed, like the top design. I'm guessing maybe they've designed it without benefit of someone on the design team who has experience with external frame packs. People certainly rave about the comfort, though.

I wish I had the metalworking skills (and a shop) to experiment with this. The traditional external frame pack updated with lighter materials and a few tweaks might be a winner.