Look up:
Frost King - Duct Insulation
Self Adhesive Foil and Foam
http://www.lowes.com/pd_28929-1410-FV516_0__?productId=1081449
Do a Google search and see what others are saying about it compared to the expensive Dynamat stuff
Like I said earlier............ I have used 10, maybe more, rolls of this stuff.
Its is a grey foam lined with a nice thick foil on top.
A few years ago, the glue was VERY WEAK. It would not stay put....... forget using it in a car, it would not even stick to itself or a duct.
So I came up with using the 3M spray tack adhesive to stick it on. It did well then.
Recently, like a month ago, I bought this again. The adhesive is VERY nice and strong now. However, if you pull it to reposition it, the adhesive grip suffers.......... of course.
Since this stuff is a foam type material, I do have concerns of it holding / absorbing water.
Also, although this stuff works REALLY well, it does not seem to have the same sound deadening IMO as the intended products. (Dynamat)
I did my old Ford Excursion solely with this stuff years ago, it held well.
Since then however I have come up with a new, different way to apply this stuff.
Today I use the Duct Foam FIRST.
I cut it into smaller strips (size contingent on application). Then COVER the Frost King with a larger sheet (one piece) of B-Quiet Ultimate.
This stuff here.
http://www.b-quiet.com/ultimate.html
The result 2X the sound deadening power, with less material used.
Also, water absorption is NO LONGER a issue, as the B-Quiet covers the foam underneath it.
ON A SIDE NOTE:
I use Frost King on areas, that may require fututre service........
Access Holes, Window Motors, Around SRS sensors, etc.
You don't want to put B-Quiet, or Dynamat on those places. IMO
When you go to pull a window regulator, you will have a GOOEY MESS to remove first.
My advices is use Frost King in these places as it is very removable later on. Cover this with B-Quiet and or Dynamat.
Think of BACON STRIPS. Frost King
Covered up with Bread...... B-Quiet.
The above is MY OPINION for the most part, It is what worked for me over the years, as I have done a few vehicles like this now.