Sometimes you will find that the inside of your windows might appear to be foggy or have a mist inside. This could be unsightly, and also lessen the transparency of the window. Double pane windows have a layer of gas inside to insulate them, and this gas is sealed in by a seal containing silica desiccant to keep moisture out. If this seal fails, the window needs to be repaired or replaced to fix the problem.
With the gas inside of the window compromised, the window will no longer be as well insulated against the outside temperature. Even if you don’t notice condensation inside your window, you can use a thermal imaging tool, and this will show you where there are differences in temperature, which either means that the seal has failed, or you have some other leak that is causing a temperature difference.
These seals will break over time due to the way the gas expands and contracts when heated up and cooled down. Naturally, better quality windows will last longer.