rigid insulation and vapor barriers

[randy41]

this is a bit confusing to me. there are generally 2 kinds of rigid insulation. there's eps and polyisocyanurate. how do they deal with moisture? is eps unaffected and polyiso needs a vapor barrier? is the covering on polyiso a vapor barrier?
i am building a walk in cooler and researching insulation options. the rigid insulation will be used in conjunction with roxul. i read 2 articles online and they are contradictory.

 

[SpringHollow]

The foil insulation on the poly is a vapor barrier. It is best to foil tape any seams. EPS will let vapor pass through.

Ken