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R- 7.8 , 2-in x 4-ft x 8-ft Faced Polystyrene Board Insulation

Perma "R" Products R- 7.8 , 2-in x 4-ft x 8-ft Faced Polystyrene Board Insulation

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Does this product have a vapor-proof layer on it, or do I need to add one with it?


The plastic coating on some poly sheets constitues a vapor barrier. The cellular nature of styrene makes in naturally resistant to moisture migration but the seams between sheets will need to be taped to complete the barrier.

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It usually has a poly film on it but I always use 6 mil poly layer over it.

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