Thermal Barriers is a long and diverse subject. They can be made from anything fibrous. A simple thermal barrier may consist of the use of a combination of wood substrate and cloth material.
However, a combination of materials, thickness, even exotic metals, and ceramics can be engaged with profound results when using No Fire Technology compounds. As you can tell this subject is deep, imaginative and continually experimental.
Ex. Spray or soak cotton strips to wrap around header pipes where the most extreme heat emanates from under the hood. Some have used soaked cotton as a thermal battier under the hood itself. Also can be used on wood that is sprayed, brushed on or soaked then layered with treated cotton material.