Originally Posted by mitiempo
You have resurrected a very old post but here is a link to the product I sell in Canada. I am not sure where you are located. The link is from Jamestown Distributors in the US. It is a high density fireproof foam in 2 layers with a mass loaded vinyl between them. It is covered with a foil surface and a which is easy to keep clean. It is sold with a mounting system and usually contact cement is used as well. It should be available where you are located. Hope this helps.
Soundown Composite Insulation Vinyl/Foam Sheets
Here is a link to a pdf showing the product details.
This is same stuff I have been considering for my generator cabinet. It's one of my winter projects. Unfortunately it's a bit on the expensive side, but it is the correct product to use.