The Stovebolt Site Forums The Shop Area Interiors Confirm - insulation foil towards heat?

Sorry, dumb question here. I bought single sided foil backed padding several years back, it has no instuctions. I plan to use it on my firewall interior. The foil side goes towards the engine side - with the plain insulation towards the interior correct?

That's the way I would do it. I'm not an expert by any definition but foil is used in other applications to reflect heat back so putting it on the hot side makes sense to me.

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.

Foil-side (or other vapor barrier-side) on house insulation usually goes on the inside-of-the-house side. However, that rule changes depending on which air mass is the most likely to condense and which side you provide vapor escape (dependent on the climate in which you live).

In a car/truck, the foil side probably serves a different purpose than it would in a house. I'd look for single-sided padding of similar construction and see what the manufacturer suggests when used in a vehicle.

Ok i used heat shield & sound deadener. part no. 25070 & the instructions say installing in engine compartmeat & floor boards aluminum foil is always towards heat. Any other applications, the aluminumfoul faces out.

Thanks, Tim. I should know better than to compare anything in a house to anything in a car!
Joe

Thermodynamics don't know where they are being applied - car, house, spacecraft, etc.

The foil goes to the air space side. If there is no air it does not prevent radiant heat transfer. In your case, there is not really an air space but I'd go ahead and put the foil toward the cab. Against the firewall it has zero chance of blocking heat, against the carpet pad or carpet back, at least there is some limited air space for it to function as designed.

Tclederman, in a house the foil side of radiant barrier plywood goes to the attic when used on a roof deck, and towards the outside when used on walls. Both cases provide an air gap at the foil to allow it to work. I've never seen foil facing on insulation unless you're referring to XPS rigid foam sheathing in which case again the foil faces out. But you're in NY and I'm in TX, and as you said, different climates use different methods, either way, the physics are the same.

maybe look up and contact seller/supplier and ask?

Thanks everyone for the replies. Depending if I have enough I'll double it up on itself, half foil in, and half foil out. Otherwise I think I'll try the foil side to the inside. I had a 48 dodge sedan that was always too hot inside, I used it on that with the foil towards the firewall and didn't notice much difference. It may be I just have the "el cheapo" product. Thanks again.