Polyiso with asphalt backing – GreenBuildingAdvisor

Hi,

I was planning on insulating my basement walls and slab. It has never been wet or showed signs of water intrusion in 10 years. I have found a good price for polyiso with asphalt backing on Facebook marketplace. I don’t know the properties with the asphalt backing. Will it be vapor impermeable at 2 inches. 

Thanks