Why is the air above an astro-turf baseball field 20 degrees hotter than the 'actual temperature' at game time? It's because the turf REFLECTS the heat BACK to the air above it. And as you move further and further away from the turf (in a vertical direction), it gets cooler. And at some point, the temp above the turf = the temp at game time.
YET, under the turf, it's 20 degrees COOLER than the air above. So if I lay a plywood sheet that's painted black on the turf, you're saying that the sheet will never approach the temperature outside? And that the turf underneath will not reflect any heat BACK to the sheathing? OK, substitute the turf with this 'foil' or RB. The heat is going to move through the sheathing to the COOLER side, yet, get reflected BACK up. This will super-heat the sheathing, no? Still, what am I missing here??!