I just checked it out on Dynamats site. here is what they had on Extreme liner
"Extremeliner provides maximum low-frequency attenuation and heat resistance. Extremeliner is a four-part composite barrier consisting of 1/8 inch layer of neoprene, 15 mils of acoustic lead barrier, 1/4 inch layer of high efficiency acoustic foam and a 3 mil urethane top facing. Extremeliner works anywhere on your vehicle's floor and firewall for the ultimate barrier from road noise and engine noise. Great for high heat areas.
NOTE: Extremeliner provides maximum control when applied over Dynamat Xtreme."
So I guess it is good for high heat areas. Also good that it blocks low freq noises.
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