Insulating glass is created by bonding two panes of glass together along their perimeter while maintaining a (usually) 1/2- to 3/4-in. space between them.
Insulating glass in windows and doors has to put up with a lot of abuse. The seals have to withstand slamming and banging. They have to be flexible enough to allow the panes to contract in cold weather and expand in hot. The seals can’t stiffen and become brittle in the cold or soften and ooze when it’s warm. They have to stand up to wind, hail, rain, damaging ultraviolet rays, age and atmospheric pressure changes.
