The main thing to pay attention to with sound deadening material is the adhesive properties. Alot of material out there isnt made to be applied to the roof or trunk lid because of the adhesive the manufacturer uses.

Im a former Dynamat rep, own a demo vehicle, and built several of their demo vehicles, so I might be a little biased. Dynamat does spend alot of R&D in their adhesives. I will say Dynamat Extreme is the most adhesive of the bunch, and working with it over several days in a row did result in some painful skin loss on my fingertips.

When applying the material to your roof, use a heat gun and you must roll the material with a roller to be effective. Otherwise it will eventually sag on its own, and this whole process would be pointless.

With the Dynamat vehicles I used Dynamat Extreme heated and rolled onto the roofs. Then I also used Dynaliner fixed onto the back of the headliner with spray adhesive. Its pretty thick and makes the headliner a little difficult to get back in, but the dampening is worth it. Most of the vehicles I treated like this, showed significant improvements. Imagine driving in the rain and the only noise you hear is the rain drops hitting the glass.