Don, I think "Thermo-Tech" is the stuff I have. I bought a small sheet at first, but over time kept finding more uses for it. So eventually I bought a much larger sheet.
I've given a lot of thought to heat management for automobiles. In the world of physics, there are basically 3 types of heat transfer; conduction, convection, and radiation. If you are interested in reading more, look at this:
http://www.physicsclassroom.com/class/thermalP/Lesson-1/Methods-of-Heat-Transfer
There are several products or techniques that I consider effective, and many that I don't:
Having parts professionally ceramic coated works pretty well, partly for heat containment (less heat escapes the hot part), and partly for excellent corrosion control (parts won't rust no matter what they are made of or how hot they get). This would be best for exhaust manifolds. But it is rather expensive to have done. There are additional types of "coatings" but they are pretty specialized and even more expensive.
The low dollar version is to wrap the part with "exhaust wrap" (ceramic fiberglass roll). This contains heat pretty well, but it also traps moisture / condensation. So corrosion becomes a big issue. This would work well on stainless steel components (won't corrode) or over ceramic coated parts (corrosion protected, plus double insulated). Good for stainless headers.
The opposite of "heat containment" is to reflect and / or insulate the heat away from a "cold" component. The Thermo-Tech mat we already discussed earlier works well for this. There are various other types of similar products; some work better than others and are usually priced accordingly. This method would be best for under intake manifolds or over sensitive parts (electronics, plastics, hoses, wires, etc). A good one for hoses, lines, wire harnesses, etc is a tube made of such materials that slips over them.
Another important aspect of heat management is to reduce the transfer of heat between hot and cold components with good air circulation. Continuous flow of cool air through the area carries the heat away. Some of the products mentioned above (heat reflection / insulation) require a layer of air between them and the part being protected, so look at the directions. If such a product is applied in direct contact it becomes very ineffective.
Ultimate protection would be to do all of these methods; contain the heat within hot components, insulate the heat away from 'cold' components, and further reduce the transfer of heat between those two with good air circulation.
Your heat shield is an example of reflective protection. Adding the insulation layer (as discussed) makes it much more effective at this. Put it onto the "hot" side of the shield. But you can carry the protection further by adding any of the additional means of heat management described here.
The X has a real problem with heat build-up in the engine bay. So consider other components that can also benefit from better heat management.