That product may be a foam that shrinks with heat (is it Styrofoam?). Also, if you leave gaps when you install it, it may not deaden sound at all. The doghouse fiberglass can act as a resonator so you need a dense thick product like a rubber mat that can take the heat. It's a fair amount of work to get it done right so don't cheap out on the proper material. HEAVY and DENSE. The foam boards work for heat transmission not sound deadening.
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