I've been a car upholsterer for 40 years...I've not seen anything better than Dynamat....factory sound deadening works by muffling the sound while Dynamat stops the panel from resinating and acting as an amplifier, then you need an absorbing layer like underlay over top of that...it takes several different layers to truly deaden the sound, it's a case of how far do you want to go....I sound proofed a 1938 Hudson, the trunk lid was like tapping an empty 44 gal drum, Dynamat over about 75% of the lid, it was then like tapping a solid timber table!! beware of some of the cheaper imitations of Dynamat, just finished a Fairlane where the guy used a cheapy in the trunk....it was already lifting off...some things are expensive for a reason!!