I had an idea for a new kind of UL backpack that probably takes us back in time 200 years. Imagine taking your wool blanket, rolling your gear up in it, tying the ends, and slinging it over your shoulder. Easy and lightweight. I did the same thing but with tyvek, essentially creating a tube that tightens at both ends and has openings down the edge to be able to access things as you're walking. It uses a single piece of tyvek, two drawcords for the ends, and several stitches along the length of the tube but perpendicular to the tube. It weighs 4 oz (100g), has a 50 liter capacity and can be worn over either shoulder.
Here are some pictures:



I would reckon it is comfortable up to 15 lb or so, and you can always switch shoulders. Downsides are that it slightly inhibits pole movement on one side and that thread holes may grow over time and weaken the fabric. It is also not well-suited to carrying bulky sleeping pads.
Advantages are that you can access any part of your pack at any time by sticking your hand in the fold at the right place, so packing your stuff carefully isn't such a big deal anymore. Just be sure to balance the weight at each end.


