Perlite Vapour Resistance!!!?

Question

Does anybody know the vapour resistance value of Perlite?

Answer 1

If you mean perlite used as insulation in walls, almost nothing, it is very pourous and air can blow through it even when compressed (as between screens).
"Although still popular, its low R-value of 2.78 per inch, and tendency to absorb moisture has lessened its popularity"
http://www.benchmark-inc.com/articles/Perspective%20Articles/issue32a.html