That's right, I forgot about the "Hood Blanket" thread.
My truck is a 1995 Chevy S-10. You could get those with the 4.3L or 2.2L engines. Mine is the smaller, which is nice because there is a little more room to work around it.
The insulation that was on the underside of my hood was pretty much gone already, just from the typical winter field mice activity of the last few years.
I pulled out the black plastic "nails" that held in what was left of the original hood insulation and used it as a template to make a new one from radiant barrier - a combination of mylar and bubble wrap.
I left the radiant barrier insulation a little long, so that it could wrap down past the hood hinges. Then I made a few cuts so it could get rolled back, specifically where is came close to the engine or exhaust manifold.
I already had an inexpensive outdoor thermometer unit that is battery-operated, so I temporarily pinned it inside the engine compartment (with the green Eco-clamp) to see if I could get temperature data. (While I do own a ScanGauge, the truck does NOT have OBD2, so I can't use that for temperature info.)
Also, the thermometer is wireless, and conveniently broadcasts to inside my nice warm house....
I'm running my 400 watt frost plug block heater right now to see if I can get a trackable difference in air temperature inside the engine compartment.