This article is from the Car Audio FAQ, by Ian D. Bjorhovde (firstname.lastname@example.org) with numerous contributions by others.
In this question, "Dynamat" refers to all commercial products that are
marketed expressly for reducing ambient noise in the car. Dynamat,
Stinger RoadKill, _et al._ all have similar pricing, so this question
is intended to give non-standard options.
There is a material known as "Ice Guard," which is used by roofing
contractors. It is similar to Dynamat, both in thickness and density.
It is self-adhesive on one side, and seems to work very well.
Unfortunately, it is sold only in large quantities (225 ft^2 rolls),
and runs about $70 for this much. Perhaps a few people could get
together for a roll, or it might be possible to get scraps from a
MCM Electronics (see Section 5.2), sells a product called
"Sound Deadening Pads" (part #60-2010) which cost $0.90 for each 10" x