You can also rip off the back of a lumbar pad like this:

https://www.amazon.com/BDK-Multi-use-Lumbar-Support-Cushion/dp/B00HXPO4FC

And put it on the pack to make your own arc haul version (zpacks bag) in a smaller weight and avoid the back sweat issue. Usually weigh 4-5 ounces. Sure there are lighter ones out there with less bulky metal frames.

Would love to find an ultralight version that's an ounce or so. Drop a comment if you know one :)

Trick I learned from r/ultralight.