I love this whole topic and how it has gone.
A few posts back there was mention of using either cork or vermiculite as an alternative to sand (or any other solid, I might add). From my perspective, this would be the way to go in terms of using an isolator that is composed of a bunch 'o small particles (sand, lead shot, etc.). The solid particles have a very high density: typical silica sand has a density of around 150 to 160 pounds/cubic foot. They are solid, and definitely not compliant. Unless they are loosely packed, they will transmit vibration due to point-to-point contact when packed. Using a less dense material that has some actual compliance could make all the difference.
I think this makes sense based on my recent review of the various isolators in the Music Direct catalog. Assuming that any of these things actually work, and I suspect that some do (although I would not know as I have two kids in college and I cannot afford them. The isolators, I mean. The two kids in college are enough, thank you). There is a common thread amongst most of them: whether they are composed of some material with "give" (Sorbothane, etc.) or a mechanical combination of springs and ball bearings, neither of which is a solid of high density. A few are, but they seem to be mostly composed of carbon fiber, and carbon fiber seems to be the panacea for everything that ails society these days so I am conveniently ignoring those.
Hacky Sacks are sounding better all the time
I am satisfied so far with my bags of hydrated bentonite. :yes: They are in my price range. You can pick up a 40 lb. bag of bentonite for about $12 at most well driller or irrigation contractor supply yards.