My son is living in a room in my shop and suffering from our current So. Cal. Heat spell. We plan to use a portable air conditioner, but currently there is no insulation. (No ceiling either.) The roof is metal and fiberglass panels exposed on the inside. Since the whole roof is due to be redone in the not to distant future, I’m seeking a temporary solution. I thought of ridgid panels cut to fit. As these would be exposed on the inside I thought I’d use poly-faced foam with a reflective face on the outside. All the edges would be foamed to form a tight seal. I believe this is styrene foam. I think this is a R-6 product. Would a higher R value foil faced urethane be better? How would it fare exposed on the inside? If we opt for the styrene, would we do almost as well with a thinner panel?

My own feeling is that sealing everything up tight will make more difference than the R value. The walls are uninsulated stucco inside and out.

Any thoughts would be appreciated.