The best fix I've found for radiant heat from the engine bay is to either pull your exhaust manifolds and down pipes and send them out for a high temp coating or purchase a set of headers. Some headers already come coated while some have to be shipped out to a vendor. If your parts are new many companies will give you a lifetime warranty on the coating but there is no warranty on used parts. Jet Hot has been my coating of choice for no other reason other than I've used their product and it works. There are other companies out there (HPC High PerformanceCoatings) that do the same thing.
Jet-Hot Extreme 2500 | Jet-Hot High Performance Coatings
The coatings make a huge difference. I can put my hand on a coated header and feel the heat immediately after shutting off the engine. It hurts but it won't scald or burn. The same header uncoated in the same situation has stripped the skin right off of my knuckles after an accidental brush.
You can cheap out and buy header wrap but be prepared to pay some extra $$$ down the road to replace the wrapped pipes when they fatigue. Oh, and you can't wrap the manifolds with header wrap...