I'm told that the insulation actually amplifies sound instead of deadening it ... because your track is in direct contact with it, akin to wood and paneling ... sounds aren't as loud if separate from it, but strike a tuning fork and press it's base against the wood and it conducts, and even amplifies, the sound. I can understand this argument because I'm a finger-style guitarist (since 1969) playing an acoustic guitar. But it's been said to use cork as your roadbed on top of that for the actual sound deadening. The foam board is mostly used for allowing you to sculpt (for landscaping, making ponds, ditches, etc.) I'm almost positive someone else will chime in on what I just typed.