Seal failure occurs when the sealant between the two lites of glass separates, subjecting the airspace to the surrounding environment. Since the sealant acts as the moisture barrier, if the seal breaks, condensation can develop in the airspace of the insulating glass window.
Its external environment such as temperature and air pressure can affect the environment inside an insulating glass unit. Changes in temperature and air pressure put additional stress on the insulating glass unit's seals. The use of less resilient sealant in the construction of the insulating glass unit can also cause the seals to fail.