Cut the noise
Crutchfield Customer Review (What's this?)
Installed with new speakers so the really good sound is due to both this and the speakers. Very expensive per square foot but seems to cut some road noise. My truck was fairly quiet to begin with. The instuctions have you cut out the hole for the speaker. Use this piece elsewhere - might as well reduce background noise as much as possible.
Pros: Deadens road noise. A huge problem for most of the cars today.
Cons: Had to cut the material up in many pieces and used material for 2 speakers on 4 because of the unusual metal pieces that the speakers mount on in my old truck. Expensive.