A vapour barrier is often used to refer to any material, typically a plastic or foil sheet, that resists diffusion of moisture through wall, ceiling and floor assemblies of buildings. Technically, many of these materials are only vapour retarders as they have varying degrees of permeability. Water vapour moves into building cavities by two mechanisms: diffusion through building materials and by air transport (leakage), which is usually far more significant and problematic. A vapour retarder and an air barrier, serve to reduce this problem but are not necessarily interchangeable.
Vitreous tile: Tile with water absorption of more than 0.5 percent, but not more than 3.0 percent. Vitrification: The progressive reduction in porosity of a ceramic composition as a result of heat treatment, or the process involved.