What's this black thing under my carpet?
 

I've attached a picture. It shows a black pad-like thing that's under the carpet, on the passenger's side front seat. Opposite the black side is a spongy material. What is it? Do I need it? If so, is there somewhere I can buy it online?

I've had water issues and this black pad thingy and the carpet have gotten soaked repeatedly. I'm going to replace the carpet and I'd like to replace this black thing too. The Honda dealership quoted me $741 to replace the carpet, but I found one for $125 here: 01-05 Honda Civic Carpet 4 Door 2001, 2002, 2003, 2004, 2005

Thank you for your help.

It is just padding. It might help make the inside of the car a little quieter, but other than that you don't need it.