Howdee , I do a lot of walking to get back away from the road warriors -so- a sandbag rear rest is out of the question. I've did some research on 'fill' materials i could use and the best 'idea' so far is round-ish cork media -problem is it's not real round and i'm afraid it won't squeeze up and hold very well if it's not smooth and round. I called a few makers of 'corky's' and such -who make fishing products [cork and plastic beads] that look like salmon eggs -they were not even remotely helpful -answer was -no we don't won't do that.Sounded like they suspected a hostile take-over of the corkys market.. Plastic beads are too heavy. I'd like to find a product 'filler media' i could use for a rear-bag and possibly camp pillow --any ideas ???? what might work?????