@@peteclark9881 you guys nailed it...double the bag capacity and blowing in front of the opening ...called the Bemoullis s Principles. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-LPpbiG-jTWI.html
Nice review, thanks. I could see using this as a replacement for the dry sack that I put my sleeping bag in. As you stated, it's a dual purpose bit of kit, and I like that.
While the info was decent, it took me a grand total of 10 seconds to figure out why my pump house ultra was "duel lined". It should have been common sense that it was to expand the size of the pump so it would take a lot less effort and time to fill out the bag.
I use mine as a clothing bag which usually means just sleep clothing. I then stuff my day clothing in and it becomes a great pillow. The material is soft enough, I don't feel the need to wrap it in anything. Because it does triple duty for me, I do take it light backpacking. My base weight is about 17 lbs.