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-   -   Pern value of 8 inches of open cell foam (http://www.diychatroom.com/f19/pern-value-8-inches-open-cell-foam-67433/)

millertimeny 03-23-2010 11:28 AM

Perm value of 8 inches of open cell foam
 
How do you calculate the perm value for a given thickness of open cell foam?

I found Open Cell spray foam has a "perm ratings of approximately 16 per 3 inches thickness (up to 30-35 perms at one inch)"

What would be the perm value for 8 inches? I'm trying to find out if 8 inches of open cell foam would be better then 3 inches of closed cell foam for a vapor retarder.


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