Here is a quick tip about constrained layer damping systems (which is what all mat type damping products are). Its not just about the added mass, but the interaction between the adhesive layer and the aluminum backing.
You need an adhesive layer that remains pliable and sticky, and a backing that is as ridged as possible, as its the shearing interaction between the adhesive and the backing that reduces vibration and noise above and beyond a simple mass loader.
If you use a cheap mat type product, the adhesive layer will harden over time, or even worse, loose adhesion. Additionally the aluminum constraining layer isn't thick or ridged enough to get the job done. Asphalt based mats, like virtually any of the cheap products on the market, don't hold up over time. The good ones simply get harder as they age, the bad ones melt or loose their stick. On top of that the aluminum constraining layers are usually only 1-3 mills thick, which isn't thick enough for the job.
A high quality mat will use a Butyl based adhesive with a nice thick aluminum backing...typically 4-8 mills thick. The thickness of the butyl layer is not as much of a concern as the thickness of the constraining layer, so 45-60 mills is usually plenty. Anything more, and you are just adding weight.
With a really good mat, you don't actually need to use that much, just enough to barely cover the center of large flat panels. Panels with complex bends already have increased rigidity and are less prone to resonance and vibration. Mat type damper products reduce vibration and resonance, which can have a secondary effect of reducing a bit of road noise. But for true sound absorption or blocking, you are looking at a different set of products.
If your goal is to block external noise from entering the cabin, then a nice mass-loaded vinyl with a decoupling layer is what you need.
Anyways, here are a few good damping products. Remember, these are anti-resonance mats...so you don't need to cover every panel. Its a lot cheaper then most realize if you use a high quality product.
CLD Tiles (Sounddeadenershowdown.com)
(8 mil foil layer)
Second Skin Audio Damplifier and Damplifier Pro
(6.5 mil foil layer)
Dynamat Extreme
(4 mil foil layer)
RAAMat BXT II
(4 mil foil layer)
The current version of E-Dead has a butyl based adhesive layer, however it uses a plastic (mylar) constraining layer which simply isn't effective. All this product does is increase mass. Even worse is the butly layer often separates from the mylar layer...I know this because I have over 50 sqft of the product in the next room and on my car. Just say no to E-dead in its current form. I've also used their older product, the one that was asphalt and aluminum. It hardened after a few years, eliminating any of the constrained layer benefits. Unfortunately this is going to be the case for just about any asphalt based product, including roofing products like peal and seal, fatmat, and any of the other cheap mats. I'm not saying they won't work...they certainly add mass, but they won't be as effective as a true constrained layer damper.
