The data sheet on GreenSkin is located here.
Devcom GreenSkin Heavy Duty Crack Suppression/Isolation Premium Flooring Underlayment - GS-4000CSI
The listed Perm rating is actually lower than Noble Company's Noble Seal TS and is labelled at 0.0011
GreenSkin Flooring also lists crack surpression up to 1/2" ! Wow That must be the best in the industry.
I'm going to have and look into this product and see how it does head to head with Noble, Ditra, Spider Web2, and Laticrete's new product.
I wonder how thick it is. I would bet in the 40mil range with a perm rating like that.