Vapor barriers must have the ability to stand up to construction.
Permeance, tensile strength, and puncture resistance are essential properties of an under-slab vapor barrier/retarder.
Puncture resistance is a critical factor during installation, but once the concrete is placed, maintaining low permeance is what provides long-term moisture vapor protection for a building.
Seams in a vapor barrier must overlap and be taped and any penetrations must be sealed.