I know many sound deadeners are just heavy, which would hurt the gas mileage. But has anyone done anything with a lighter weight deadener or something to help cut back on the in cabin road noise? If there is a thread out there on this already for the C, please point me in the right direction.
I added some of this to the C and to the Gen II Prius, the Gen II had a door rattle driving us crazy, and the C; well you know it is a bit loud with certain road conditions. 30SQFT Five Door Kit 12"x36" Sheets Gtmat Pro 50mil Car Sound Deadener Material | eBay I also added the foam one in the C doors... Has not affected mileage.
Yeah Dynamat but you gotta watch out for the heavy rubber types, I thought someone may have already investigated a lightweight sound insulation. I'll have to look around.
Check out Summit Racing's house brand sound deadening. It is supposed to be as good as Dynamite, but much cheaper. Posted via the PriusChat mobile app.
I can't speak for the Prius C, but I used 50 mil Noico in my 2nd gen for good results - outside and wind noise were significantly reduced. However there's still a lot of noise coming through from the suspension and wheel wells. Definitely helped, but my next upgrade is to get quieter tires. With such low cost options now available, Dynamat is way overpriced IMHO. If you want to treat all 4 doors with about 75%, you can get this kit: Noico 50 mil 25 sq ft. It comes with 12 sheets, so you can use 3 per door, or you might get better results using 3.5 in the front doors and 2.5 in the back. I believe it's only 11 lbs. If you want even better sound treatment for a bit more $, you can get this kit with thicker layers and enough to treat your doors and tunk area: Noico 80 mil 36 sq ft. Also one trick that I did is to seal in the inside of my car doors by cutting out shapes of 3/8" hardboard and fitting them to the large holes on the inside sheet metal. Doing this you can form a (nearly) sealed enclosure on the inside of your doors, which will add another layer for blocking sound. This will also improve the bass response of the door speakers, and improve insulation of the car reducing A/C load slightly. See picture:
