NPD sell a whole car kit for half the price as mustangunlimited, same stuff, and the pad for the just the trunk for $10.

 

Everybody sells carpet underlayment, but not everybody sells this stuff. Steve linked to regular underlayment for a vert. Where can a guy get the original stuff?

 

I have not seen the original type stuff for sale. It's almost like a 3/4" gray pad w/multicolor particles. You don't see the original onesb/c they held moisture and caused rust to form around the tank. I think they were standard on convertibles. I don't use anything under my rubber mat but I don't drive it everyday so the added noise does not bother me.