Insulated Glass 
What is insulated glass?
Also called double-pane glass, it consists of two pieces of glass, with a moisture-absorbing sealant between them. Insulated glass can only be installed into windows or openings that are prepared for this purpose.
What causes fog or condensation in between the glass in your windows?
When the seal between two pieces of glass breaks, it begins to let in air. The difference between the temperature indoors and outdoors causes condensation: moisture collecting in the space between the two panes.