Recently I went to purchase some good quality polyfill for some small bookshelf speakers i was building. I stopped at Good will as they sometimes have bags of it for sale. I happened to pass a bunch of used sleeping bags and noticed there was a large weight difference in identical sized bags.
Upon closer inspection I discovered that the better "bags" used a much more dense material. Same stuff basicly,just more dense. I paid $4 for a single bag containing 6 pounds of "800 hollowfill". Thats a lot of weight for a small sleeping bag. Tell me I'm crazy,("you wont be the first!) ,but I noticed a marked difference in the damping ability of this material over normal poly fill.
I guess my point is that I feel this may be a way to buy some seriously superior damping material for a fraction of the cheap stuff. You might want to
steam it however....cant imagine how I would explain to someone how I got bed bugs in my speakers!!!