http://www.cascadeaudio.com/damper.html

from the site:
Quote Originally Posted by cascade
VB-2 is a flexible, odorless and lightweight mineral filled vinyl-copolymer formulated to handle the demanding extremes of aircraft vibration and noise control. It has twice the damping and less than half the weight of asphalt damping materials and the ability to handle continuous temperatures to 250 degrees.
i picked up a 4.5sqft roll from ABC warehouse for $25 as an alternative to dynamat extreme door kits. it came in a 12x54" roll. a lot more deadener than typical speaker kits.

install was simple and like every other damper. lay out the piece, cut to fit, clean the panel and apply. a bit of heat from a hair dryer helped to get the material to bend into curves and get 100% contact.

after install, the area around the door is now nice and solid. when thumping it with a fist, resonance is eliminated and all you get is a nice solid "thud". as with other door kits, the speaker response is much better with mid/bass greatly improved.

A+ product, i'd highly recommend it