Engelhard (now BASF i guess) has 4 different sizes of glass microspheres.
"Prizmalite Ultrafine glass microspheres"
4micron P2011SL $39/kg
10micron P2015SL $38/kg
38micron P2043SL $9/kg
50micron metallized glass microspheres P2453BTA $75/kg
The last time I made some sound deadener messin around, I used 4micron 12% by vol and 50micron 8% by volume in a latex neutral base.
I mixed my arm off. In the end it seemed like it could have held more, but I didnt have a pressure pot at the time. When you go shopping for paint, find the thickest neutral base. No pigment. Then color the last coat if needed.
I have 4kg of of P2011SL left. $20/kg if anyone wants some.
I also did another method using glass beads from highway paint. These are much bigger (and probably not 'beads'). For the sake of this I will say 150-200microns.? I sprayed an offroad only 4x4 with these for visual purposes. I sprayed white base, then mixed some in clear. But these are so heavy, the clear wouldnt hold hardly any, or else I would have had to spray 30coats to get the desired concentration. So I would spray on a slow clear, then use my flakebuster and hose on the glass beads. Worked much better. I did this till the concentration was 100%. Probably 4coats.
As far as sound deadener, that definitely worked, although that wasnt the intended purpose. I figured durability would suck, but its been great so far. If you rub something against the paint job like say a chain or jack, it just glides on the glass beads. Feels pretty kewl. But, if a moron loses his brakes on a hill and t bones you, it does fail.