In the early 1980's I used one of these in the British Army. A local company was selling them with the straps replaces by a US M1956 webbing yoke stitched to the pack. It was very comfortable and being of limited size forced me to think about what I was carrying and it was light years ahead of the 58 pattern large pack.
No idea what the material is in all honesty,thought it would be some form of cloth based duct type tape but seems to be some form of nylon type material(cannot rip/tear it like duct tape)