Siding question

I think it's an insulation layer.

Probably foil faced rigid foam insulation.

From:

"... Polyurethane and polyisocyanurate are both closed-cell foams that contain a low-conductivity gas in the cells (usually one of the HCFC or CFC gases.) The high thermal resistance of the gas gives these foams an R-value of between R-7 and R-8 per inch. ... Foil and plastic facings on these foam panels help to slow the escape of gas from the cell structure. Testing suggests that the stabilized R-value of rigid foam with metal foil facings remains unchanged after 10 years. The reflective foil, if installed correctly, can also act as a radiant barrier (another type of insulation) that adds about R-2 to the insulating assembly. Panels with foil facings have stabilized R-values of 7.1 to 8.7 per inch. ..."

John

But this extra value is based on about 1/2" spacing above it. In theory, Double Duch siding should provide this, but that 1/2 inch needs top be sealed. Still, there should be some extra value there.

Panels with foil facings have stabilized R-values of 7.1 to 8.7