Open-cell is suitable for hard-to-reach places such as existing attics. It is also an excellent option for soundproofing. However, open-cell does not create a vapor barrier. 

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Closed cell has the highest insulation value (R-value) per inch of any insulation type. It also seals to create a vapor barrier to your new or existing building. Closed-cell is versatile because it can be used in walls and attics built with wood, metal, or concrete. Closed-cell is also an excellent option for crawlspaces and below slab.