Extruded polystyrene boardstock and roof structure containing the extruded polystyrene boardstock

A polymer foam insulation board comprising a foamed polymer layer that includes one or more organic polymers, the organic polymers comprising at least 70% by weight of one or more alkenyl-aromatic polymers, the foamed polymer layer having opposing first and second major surfaces and a thickness orthogonal to the opposing major surfaces;

• a first facer sealingly bonded to the first major surface to form a first outer surface and a second facer sealingly bonded to the second major surface to form a second outer surface, wherein:
• the foamed polymer layer has a foam density of at most 56 kg/m3 (3.5 pounds per cubic foot), a thickness of at least 0.6 cm (0.25 inches), an RSI-value of at least 0.95 K·m2/W per 25.4 mm of thickness (R-value of 5.11° F.·ft2·h/BTU/inch of thickness), and contains at least 0.25 weight percent, based on the weight of the foamed polymer layer, of an infrared radiation attenuating additive;
• wherein the infrared radiation attenuating additive is one or more of graphite;
• carbon black;
• soot;
• a carbonized fiber, flake, or powder;
• carbon nanotubes, fullerenes, graphene, graphene oxide, or graphite nanoplatelets,
• wherein each of said first and second facers is constituted by layers comprising films assembled into a multilayer structure, each of said first and second facers having a thickness of 19.05 to 63.5 μm,
• the layers comprising, in order from the foamed polymer layer to an outermost surface of the polymer foam insulation board, an interior moisture barrier layer facing the foamed polymer layer, a tie-layer comprising polyolefin, an oxygen barrier polymer layer, a tie-layer comprising polyolefin, and an exterior moisture barrier layer, wherein the interior moisture barrier layer comprises ethylene-vinyl acetate polymer and the exterior moisture barrier layer comprises polyethylene;
• wherein each interior moisture barrier layer has a thickness of 2.54 to 12.7 μm,
• wherein each exterior moisture barrier layer has a thickness of 2.54 to 12.7 μm and further comprises a reflective filler, wherein the reflective filler, by itself, reflects at least 80% of incident visible light,
• wherein each of the first and second facer has an opacity of at least 65%, an oxygen transfer rate of at most 0.65 cc/m2-day, an oxygen permeation rate of at most 0.9 cc-mil/m2-day, and an Elmendorf tear strength of at least 120 g/25.4 μm in at least one direction;
• and
• wherein each of the first outer surface and the second outer surface exhibits a surface solar reflectance of at least 35% as measured according to ASTM C1549.