What feature do Polyisocyanurate and polyurethane often have on both sides?

Polyisocyanurate and polyurethane insulation boards typically have a foil vapor retarder or radiant barrier on both sides. This feature serves multiple purposes critical for building performance. The foil acts as a barrier to moisture, which helps prevent condensation within wall assemblies, significantly reducing the risk of mold and structural damage. Additionally, the reflective nature of the foil can enhance energy efficiency by reducing radiant heat transfer, thus maintaining better temperature control inside the building.

The use of foil on these insulation types is a common practice because it combines insulation properties with moisture control, making it ideal for various applications in both residential and commercial buildings. The foil layer also provides some structural integrity and can contribute to the overall durability of the insulation system.