That's a darn good question and I am not saying you are wrong,Tiny ! I may well be wrong in my thinking.
I know that when decking a house for a roof, the foil goes on the underside and not toward the heat source, that being the sun. I also know that one of things that is done if a house does not need a roof is the hang foil in the attic under the rafters. So not trying to muddy the water here, but I have often wondered the answer. I am about to order some foil on one side insulation for my cab, too, and would like a definitive answer. The heat from the engine compartment is pretty intense.
