Again, based solely on the rendering, it certainly seems that way, but never having seen any 'in the flesh', no clue what the ratio might be. Note too that by 'bonding agent' I'm assuming it's a mix of fine dust plus binder same as with PB and some other composites/press board construction panels I'm aware of from my days of designing electrical systems for the pulp n' paper industry.

I did a search to see if there was any locally to look at, but found none, though this Enviroboard Altec 'sub' ad popped up down in Fla., so beginning to wonder if it was spec'd. for [near] tropic apps:
Altec Lansing AB2200 Acoustabass 12" Low Frequency Speaker System | eBay

GM