There are three types of glass panels typically used to construct modern windows: plate glass, tempered glass, and insulating glass panes.

Plate Glass

This is the standard glass normally used in house windows. It can be plain or tinted to reduce glare and can be doubled up to sandwich in a thin airspace for insulating qualities. When struck or put under stress, it shatters into pieces that are usually very sharp. It’s an excellent material for windows, though, because it can be manufactured free of flaws and distortions.

Tempered Glass

Tempered glass panes are three to five times stronger than those made of ordinary plate glass. Tempered glass should be used in doors and in glass panels adjacent to doors and other areas where it is likely that people, especially children, might run into or fall against them. In fact, many building codes require the use of tempered glass in wall areas that are within 4 feet of any door. When struck or put under stress, tempered glass develops hairline cracks or breaks into many small, rounded pieces instead of into the sharp, ragged pieces that come from standard plate glass. Auto windshields are a common example of tempered glass.

Insulating Glass

This glass exists in two forms. One is a special double or triple sheet of glass (double or triple pane/double or triple glazed) separated by an airspace(s) with the glass edges welded or formed together to make airtight center spaces much like the liner for a thermos bottle. The other consists of two or three sheets of glass held in the frame with an insulating airspace in between.

Double-pane and triple-pane insulating glass

Double-pane insulating glass used in most stock windows is made of two panes of sheet glass having a  3?8 to 1?2 inch of airspace between them. Triple-pane glass windows consist of three panes of glass with approximately 3?8 inch of airspaces between each pair of panes (see image).