.... describe the particles please? Any blown-in insulation I've seen wouldn't be appropriate because it lacks rigidity and would compact easily, but it really depends on the physical properties of the particles - how rigid they are and size, primarily. Many think that perlite increases drainage significantly, but its primary benefit doesn't come from it's rather insignificant impact on drainage/flow-through rates, but from reduced water retention resultant from the fact that it takes up space that would otherwise be occupied by small particles and the water that would be trapped between and in them.

Al