Best foam board for knee wall access doors?
 

Greetings all,

I am in the process of air sealing and improving the insulation in my attic.
I'm wondering what best to use for foam board on the access doors. The r value seems pretty low on most boards and if it is too thick the door won't open properly (think arc). So, my question is can someone recommend which foam board to use? I've seen an RMax with R9+ @ 1 1/2" but ii is intended for exterior use. Could I use this as I think three inches would be the max depth possible.
TIA

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.

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.

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