Hi bigbth-
If you are referring to the insulation material beneath the "cardboard" on the firewall insulator, I have had good results with a fresh piece of the old style carpet underlayment. It hasn't been available new for a while now, but an old house renovation is a good bet. It is a convincing repair from the engine side. The "cardboard" material is another story. There used to be an outfit that sold it in PA. (they used to sell out of the back of their truck at Hershey) called Three Rivers Supply, but I haven't seen them there for years and they don't ship through the mail.
SPEEDLINE