On my roof I'm using owens Corning 703. It's what we use in recording studios to kill sound. You can find it at an insulation distributor but not at your nieghborhood lowes/home depot. Thios stuff is 1" or 1 1/2" thick and really does the job.

1959 Chevy Apache-Suburban
5.3, 4L60e, Camaro Subframe, enjoy doing the work ourselves!
In the Stovebolt Gallery
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Driving the past into the future.