# Best foam board for knee wall access doors?



## Windows on Wash (Aug 30, 2011)

Polyiso or EPS.

The Polyiso with the foil facing is great as it provides some added benefit from the radian barrier. You can stack the layers together to get you whatever thickness you need.


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## diyxer (Jul 9, 2012)

Windows on Wash said:


> Polyiso or EPS.


Thanks, are those brand names? What kind of R value per inch can I expect to find in these?

Sorry for the dumb questions. But every time I go to HD or Lowes I'm seeing stuff that is 2 inches thick with like r3 value. That just won't cut it.


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## Windows on Wash (Aug 30, 2011)

HD or Lowes look for a Thermax board (roughly R-6 per inch).


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