gasimpermeable

Gasimpermeable refers to materials or barriers that exhibit negligible permeability to gases under defined conditions. They block or greatly slow the diffusion of gases such as oxygen, nitrogen, carbon dioxide, and water vapor, depending on humidity.

Common gas-impermeable materials include metals (aluminum foil, steel) and dense inorganic glasses and ceramics. In polymers, low-permeability options include certain gas barrier polymers like polyvinylidene chloride PVDC, ethylene vinyl alcohol EVOH, siliconized polymers, fluoropolymers such as PTFE, FEP, PFA; when used as thin films, they are often part of multilayer structures combined with PET, polypropylene, or nylon to reduce permeation.

Permeability is quantified by permeance and permeability; units include Barrer. Tests use oxygen transmission rate (OTR) or water vapor transmission rate (WVTR); equipment such as MOCON permeation analyzers; and standard conditions (for example 23 C, various relative humidities). Gas impermeability depends on temperature and pressure; some materials become more permeable at higher temperatures.

Applications include food packaging requiring high barrier to oxygen; pharmaceutical packaging; electronics encapsulation; and specialty coatings for corrosion resistance. In research and industry, multilayer barrier films and dense coatings are designed to achieve gas impermeability for specific gases or environments. Gas-impermeable materials are often selected to balance barrier performance with mechanical strength, cost, and processing compatibility.

Limitations and considerations include the fact that no material is perfectly impermeable; microdefects, pinholes, or imperfect lamination can create diffusion paths. Long-term performance can be affected by aging, environmental exposure, and mechanical stress, and high barrier performance may come at the expense of flexibility or cost.