I’ve heard that polyisocyanurate foam loses its insulation value (R-value) over time. Is that true?
Not for IPS panels, but in general, yes. The reason is that the gases in the foam placed there by the blowing agent are heavy, inert gasses that convect poorly, adding to the insulation value of the product. However, in un-faced foams these gasses leak out and are replaced with air, which convects much easier. The result is a loss in insulation value. However, the dual steel skins on IPS panels trap the gasses in place. Therefore, the insulation value does not fall.
