The Three Types Of Glass

Insulated Glass - When multiple glass panes or "lites" are assembled into units, they are commonly referred to as "insulated glass" or "insulated glass units-IGU". The proper technical term for the assembly is hermetically sealed units, meaning that the environment inside of the unit is isolated from the external environment. These units are produced with the intention of maximizing the thermal insulating properties of a gas contained in the space formed by the unit while at the same time providing clear vision through the unit at low temperatures.

Most IGUs are double glazed, but IGUs with three sheets or more, i.e. "triple glazing" are becoming more common due to higher energy costs. Insulated glazing may be framed in a sash, frame, or in a curtain wall. IGUs are also commonly used for replacement windows.

Laminated Glass - Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic "spider web" cracking pattern when the impact is not enough to completely pierce the glass.

Automobile windshield with "spider web"
cracking typical of laminated safety glass.

Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Skylight glazing and automobile windshields typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtainwalls and windows. The PVB interlayer also gives the glass a much higher sound insulation rating, due to the damping effect, and also blocks 99% of transmitted UV light.

Toughened or Tempered Glass - Toughened or tempered glass is glass that has been processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. It will usually shatter into small fragments instead of sharp shards when broken.

A vandalized telephone booth with
tempered glass

Toughened glass is used when strength, thermal resistance and safety are important considerations. The most commonly encountered tempered glass is that used for side and rear windows in automobiles, used for its characteristic of shattering into small cubes rather than large shards. Tempered glass is also used in buildings for unframed assemblies (such as frameless doors), structurally-loaded applications, and any other application that would become dangerous in the event of human impact. Toughened glass is used in some cell phones due to its scratch-resistant properties.