The whole base of the truck is actually a huge series of rollers with gaps in between allowing the contents to move based on the angle of the tray of the truck while not picking up any dirt and gravel while loading. Bumped into this new innovation at work a while, or at least talk of it. Informed about them coming to our transport industry in the near future in the big way. Good news - well look at the video, it's cool. Bad news - yeah most trucking companies just sacked a whole bunch of logistics and warehousing/loading staff. Must admit haven't seen or heard of it again more recently.
As for those rolls? Compressed bails of wool maybe?