Soldato
How does that bag prevent you from getting a sweaty back? Is it waterproof?
The bag itself is arched, so it sits away from your back. You loose a little space, but it's still 15L. The part that makes contact with you is a mesh (can see it here), so it's much better airflow than a rucksack sat on your back. Doesn't eliminate sweaty back syndrome altogether, but much better than a traditional one.
Also has a foldaway waterproof cover that zips up underneath in its own little compartment.