I bought mine at a local upholstery shop; there are several lakes not far away so they do a fair amount of boat business. Mine is just plain marine carpet, glued on without any other deadener or insulation.
When my original headliner sagged and wouldn't stay glued up, I replaced it with (gray) marine carpet. Slight improvement in both insulation and noise reduction, but not a dramatic difference. But it's never sagged or fallen off.