Insulated glass is a combination of two or more panes of glass with a layer of inert gas namely argon or krypton in between them. The two pieces of glass are further separated by an aluminium spacer bar which has holes in it; a desiccant which might be silica gel or zeolite is used below the spacer bar material so as to absorb any moisture that may be initially present in between the glass panes. A primary sealant is used on the inside to fix the spacer bar to the inside of the glass panes while a secondary silicone sealant is used on the outside to create an airtight seal along the continuous sides of the window.