Its a modified version of Gossamer Gears G4 pack. You can get the pattern on the net for free. Made my first one some years ago, and have modified it to fit me a bit better, and to hold more weight(water), and to have some extra outside compression pockets. This pack comes in a 18oz, very heavy for a light pack but the material is much stronger than Nysil. Ive made some that were 11oz! Thats my ultra light backpacking rig in water rich areas.
Its cool because the waist and shoulder straps have a velcro opening, you can stuff socks and gloves in them for padding. A Zrest pad is the frame. A bit sweaty with a heavy load but with a light on its very comfortable.