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Instead of using Reflectix I thought that I would use the R-Matte 1/2" iso foam that has reflective foil on one side. 

One reflective surface facing out next to the sheet metal and the other facing inward. This would leave a 1/2" air gap between the two.

Or would it be better to have the air gap next to the sheet metal?
I use the r-tech foam which is probably similar since it has a reflective side. Myself I put one inch (2x 1/2 inch layers) then left an air gap and put another 1/2 inch layer. 

But in everyday use, the air gap did nothing, I sill feel heat coming through. I will be redoing it and getting rid of the air gap and just hotglue the layer to the other foam and maybe add another 1/2 inch total 2 inchs of foam. I notice the more foam I add the cooler I feel inside my van.

Maybe for others the air gap works but did nothing for me. Its going to be major work re doing the job.
Did you install all layers with the shiny sides out? To deal mainly with heat and not so much when it's cold?

And was this in a cargo trailer or a van?
As shown above, there is little value in air gapping in a van, if you can afford to just fill up the space with the best-value foam, and get as complete a seal of the envelope as possible.

I just consider the foil side of rigid board as physical protection of the foam's integrity.

The "foil + air gap" technique IMO is when you've got lots of space between the interior and exterior, like in a house, and have already maxed out (5-8" foam, 12" batts) on the amount of insulation you are willing to buy.
Yes the shiny does nothing at all significant in the cold, it is for reflecting back radiant sun energy only.
(02-15-2018, 08:07 PM)slow2day Wrote: [ -> ]Instead of using Reflectix I thought that I would use the R-Matte 1/2" iso foam that has reflective foil on one side. 

One reflective surface facing out next to the sheet metal and the other facing inward. This would leave a 1/2" air gap between the two.

Or would it be better to have the air gap next to the sheet metal?

Definitely better to have the air gap next to the sheet metal.

Having the foil directly against the sheet metal does absolutely nothing for a radiant heat barrier. The heat passes directly from the van wall to the foil. It is then trapped inside the R-Matte, heating it up.

Having a foil side facing the inside of the van will only  help hold the heat in there, and only if there's a dead air space between it and the finished wall. Holding the heat in there may be somewhat attractive if you're living in a cold temperature and heating the van with a heater. Would be worst possible scenario if you're trying to keep the van cool.

Best study up on how a radiant heat barrier works. I couldn't find any manufacturers' information directly pertaining to mobile applications so I had to use their information about utilizing their product in steel buildings...same concept, different application.
To be effective the reflective surface must face an airspace. If there is no airspace install a more traditional insulation like some type of foam product with the highest R-value you can fit into the available space.



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Shiny facing low-energy heat sources on the inside in cold weather will also have zero effective impact.
I believe the foil is also the vapor barrier , so you have two vapor barrier
which generally not a good idea I thought.
What about the pink unfaced foam than a sheet of Mylar than your wall cover paneling
(02-22-2018, 09:26 AM)toddanderson Wrote: [ -> ]What about the pink unfaced foam than a sheet of Mylar than your wall cover paneling

1/2" pink (Owens) is R3.0 compared to R3.2 for the R-Matte and it's also 10% costlier. You'd also have to add in the cost of the mylar.

I'm not sure how important a vapor barrier will be on a cargo trailer. All the gaps between panels will be taped.
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