Heat..... There is a company named Lydall Thermal Acoustical that makes a product called
An innovative solution developed and patented by Lydall to protect interior components from excessive heat. This adhesive backed application is designed to protect interior components on a vertical surface.
This is used around exhaust systems in automotive to protect gas tanks and floor pan carpets. You can purchase thru these guys http://www.randallraceparts.com/otherinsulation.html
Its expensive but it works. I use it inside all my tunnels and around exhaust pipe areas. Hope this helps