I saw this on an old thread and decided to bring it back up because it said the old topic was closed.
Someone suggested trying www.mcmaster.com for a dynomat alternative. They also gave info about it and where to find it since the website is huge. They changes things around a little bit and the new page number it is on is 3302. It is about halfway down that page and called "Adhesive back damping sheet" the one to get is the polymeric mastic. It is 14.62 for a 32x54 piece. They have 5 or 6 locations so shiping is pretty quick. I just ordered 2 rolls and shipping was ony 6.50. The incredible thing is I ordered it on Wed morning at 10 am and they said I would have it tomorrow at my Florida home.
Give em a try, much cheaper than dynomat.
If you type in the words "polymeric mastic" in the search engine on the left, it takes you to it without having to find the page.
That's the stuff for cheap! I've had it installed for two years now in my car, through all seasons, and no failure. My cheap system sounds like high end SQ. And true about the shipping and cost; I ordered it one day and received it the very next morning. Cost of shipping was the actual UPS cost, which at that time was about $11 for 36 sq ft. Heavy box.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
McMaster is also good for Acrylic, Lexan, ABS, aluminum, hardware, fasteners, tools................
The latest catalog I got was 3390 pages.