what is a vapour barrier
A vapour barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through wall, ceiling and floor assemblies of buildings to prevent interstitial condensation and of packaging.he function of a vapor barrier is to retard the migration of water vapor, which are not typically intended to retard the migration of air. This is the function of air barriers.