I have a 2005 Mazda 6 with the 4 cylinder engine. An animal of some sort decided to build a nest under the plastic engine cover and used some of the insulation from under the cover. Is this sound or heat insulation? Seems that if it is sound insulation it might not be a big deal, but if it is supposted to be heat insulation, I might have to replace it. Anyone know for sure?

 

As a matter of fact, my 3 was like that when I bought it brand new in '04.
Mazda replaced the engine cover under warranty for me, but frankly I don't like them anyway. Mine has been in my shop ever since, and just in case I sell the car someday.
The insulation is so itchy that I believe it to be a form of rock wool, which is an excellent sound insulator. So that's my best guess. However, don't worry about it. I live in Texas where it was nearly 100*F today and I have never had a problem w/excessive heat.