Epoxies are noted for having very low gas permeability as well as minimal water vapor transmission properties. These attributes are very desirable in many bonding, sealing, coating and encapsulating applications. This prevents susceptibility to degradation and use as a permeation barrier against gases and liquids commonly employed in industrial applications. The key to formulating systems to optimize the effectiveness of these materials as barriers is to use resins and curing agents that maximize polymerization. Also, adding heat to the curing schedule will substantially increase the effectiveness of the barrier.
Epoxies typically have gas permeability values of 2-10 cc/m² per 24 hours and water vapor transmission at 38°C at 95% relative humidity of less than 0.8 grams/m² per 24 hours. When compared to silicones, which have gas permeability of 2,000-20,000 cc/m² per 24 hours and water vapor transmission of 100-150 grams/m² per 24 hours, epoxies are particularly desirable. As mentioned above, the outstanding performance of epoxies, in this regard, is due to the extensive cross-linking of this kind of system after curing.