Which of the following is NOT among commonly used vapour barrier materials?

• A. Concrete
• B. Foamglass
• C. Styrofoam
• D. Urethanes

Answer: (A)

Vapour barriers are materials chosen for very low water vapor permeability to stop moisture from moving through a building assembly. Concrete isn’t normally used as a vapor barrier because it’s porous and prone to cracking, which allows moisture to diffuse through it over time. Even if it’s dense, concrete isn’t reliably vapor-tight and would require extra sealing and maintenance, making it impractical as a dedicated barrier. In contrast, foamglass (cellular glass), Styrofoam (extruded polystyrene), and urethanes (especially closed‑cell spray foams) are engineered to have very low vapor permeability and can seal gaps, providing effective moisture control in addition to insulation. That combination of reliable vapor resistance and practical installability is why concrete isn’t listed among common vapor barrier materials.