Dynamat DynaPad Get rid of road noise 1 sheet, 12 square fee
This stuff is heavy and thick.  It does not have an adhesive backing.    It will be just enough to cover the entire cabin area of a car under the seats.    It is basically heavy rubber sandwiched between two layers of neoprene. (Closed cell foam.)   There is no doubt that this will provide some serious sound dampening qualities to cut road noise.   I recommend it.