Foil-faced foam board insulation (polyisocyanurate) is a vapor barrier and does not require an additional vapor barrier, while rigid foam board insulation without foil may need one.

HOUSTON, Nov. 2, 2021 /PRNewswire-PRWeb/ -- Foil faced insulation reflects up to 95% of infrared rays that land on the roof and is highly efficient at retaining interior heat within the space ...

Rigid foam for use in metal-faced sandwich panels combines the thermal insulation properties of conventional polyurethane (PUR) foam with the enhanced fire resistance of polyisocyanurate (PIR).