When doing sound-proofing on Prius, most people in this forum use Dynamat Xtreme, which is aluminum foil + butyl rubber, with a ridiculous price tag. After some googling, I found an alternative sound and heat isolation material called "Thermozite", which is made up of recycled PET, so called eco-fi (ecospun), and foil. Thermozite is way cheaper than Dynamat Xtreme, and its noise reduction coefficient(0.30) is very comparable to Dynamat Xtreme(0.417). And if thermo isolation is not of your priority, there is an eco-fi carpet padding that is even less expensive with even higher NRC (0.66). I am not from the acoustic industry and I might be very wrong. Is there any specific reason why Dynamat Xtreme is so popular? Auto Carpet Felt Padding Thermozite Thermal-Acoustic Insulation - Heat & Sound Shield http://dynamat.com/download/specs/2204_Spec_Sheet_Dynamat_Xtreme.pdf
