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Component placed at the perimeter of an insulating glass unit to separate the two lites of glass.


The controlled process for making glass stronger and less brittle in which the glass is heated and then cooled.

Annealed glass:

The most common form of glass found in residential applications, annealed glass is a standard sheet of float glass that is easily broken and produces large dangerous shards when shattered. On its own it provides very little insulation and acoustical qualities.


An inert, nontoxic gas used in insulating glass to reduce heat transfer.


Shortened term for polyisobutylene. The primary seal of an insulating unit and key component in restricting moisture vapor transmission.

Ceramic Frit

An enamel applied to glass for decorative/aesthetic appearances and/or functionality such as solar control, ceramic frit is applied with a large roller for full spandrel applications or through a screen for silk-screen applications.

Coated Glass

A general reference to any glass incorporating a reflective or low-e coating.


The appearance of moisture (water vapor) on the surface of an object caused by warm moist air coming into contact with a colder object.


An extremely porous crystalline substance used to absorb moisture from within the sealed air space of an insulating glass unit.

Double Laminated Insulating Glass:

An insulating glass unit in which both the interior and exterior components are a laminated glass.

Dual Seal

Refers to an insulating unit with a primary seal of polyisobutylene (butyl) and a secondary seal of silicone.


The measure of a surface's ability to emit long-wave infrared radiation.

Float Glass:

Glass formed on a bath of molten tin. The surface in contact with the tin is known as the tin surface or tin side. The top surface is known as the atmosphere surface or air side.

Fully Tempered Glass (FT):

Glass that has been heat-treated to have either a minimum surface compression of 10000 psi or an edge compression not less than 9700 psi in accordance with the requirements of ASTM C 1048 kind FT or meet the requirements of ANSI Z97.1 or CPSC 16 CFR 1201 safety glazing standards. Tempered glass is 4-5 times stronger than annealed glass and when broken breaks into small relatively harmless pieces.

Heat Soak:

A process of heating glass to a specific temperature for a specified time in a special oven in an attempt to find any impurities in the glass known as "nickel sulfide inclusions".

Heat Strengthened (HS):

Glass that has been heat-treated to have a surface compression between 3500 and 7500 psi and meet the requirements for ASTM C 1048 kind HS. It is ~2-3 times the strength of annealed glass. Heat-strengthened glass is not a safety glazing material and will not meet the requirements of ANSI Z97.1 or CPSC 16 CFR 1201.

Heat Treated:

Term used for both fully tempered glass and heat-strengthened glass.

Insulating Glass (IG):

Two glass components separated by an air spacer and hermetically sealed. Inherently insulating glass increases a window's thermal performance.

Insulating Laminated Glass:

An insulating glass unit in which the exterior component is a monolithic glass ply and the interior component is laminated glass.


Refers to the plastic or vinyl in a laminated unit.

Laminated Glass:

Two or more pieces of glass bonded together by a piece of plastic/vinyl called polyvinyl butyral (PVB.) A minimum interlayer thickness of .030 (.76mm) meets the requirements of ANSI Z97.1 or CPSC 16 CFR 1201 safety glazing standards.

Laminated Insulating Glass:

An insulating glass unit in which the exterior component is a laminated glass and the interior component is a monolithic glass ply.

Light to Solar Gain Ratio (LSG):

The ratio is equal to the Visible Light Transmittance divided by the Solar Heat Gain Coefficient. The Department of Energy's Federal Technology Alert publication of the Federal Energy Management Program (FEMP) views an LSG of 1.25 or greater to be Green Glazing/Spectrally Selective Glazing. 


Another term for a pane of glass. Sometimes spelled "light" in industry literature.

Low iron:

Low iron glass is a type of float glass manufactured with less iron than standard clear glass. With this reduction in iron content the greenish tint is reduced. Starphire and Optiwhite are low iron glass substrates.


An abbreviation for Low Emissivity coatings. They are applied to glass to reflect invisible long-wave infrared or heat. They reduce heat gain or loss in a building by redirecting the heat. In addition they typically provide greater light transmission low reflection and reduce heat transfer.


Refers to a single lite of glass as a finished product.


Glass unit wherein the two glass ply edges are intentionally not aligned.

Pattern Glass:

Glass with textured surface to emit light but restrict vision.

Polished Edge:

A special fabrication done to the edge of a piece of glass. Makes the edge smooth and gives it an extremely shiny or polished appearance.

Polyisobutylene (PIB):

The primary seal of an insulating unit and the key component in restricting moisture vapor transmission.

Polyvinyl Butyral (PVB):

The plastic or vinyl used in the makeup of a laminated unit the vinyl is what holds that unit together.


Thermal resistance of a glazing system expressed ft2/hr/°F/BTU (m2/W/°C). The r-value is the reciprocal of the U-value. The higher the R-value, the less heat is transmitted through the glazing material.

Relative Heat Gain (RHG):

The amount of heat gained through glass taking into consideration the effects U-value and shading coefficient. The English System relative heat gain is calculated as: RHG = (Summer U-value x 14°F) + (Shading Coefficient x 200). The Metric System is calculated as: RHG = (Summer U-value x 7.8°C) + (Shading Coefficient x 630). The lower the RHG the more the glass product restricts heat gain.


A process of applying a specific design or pattern to glass. The design is made by placing a screen over a piece of glass and then pressing ceramic frit by means of a large squeegee through the pores of the screen. After the frit is applied the glass goes through an infra-red oven to dry the frit and then through a tempering furnace to fire (bond) the frit to the glass permanently.

Solar Control Glass:

Tinted and/or coated glass that reduces the amount of solar heat gain transmitted through a glazing product. 

Solar Heat Gain Coefficient (SHGC):

The portion of directly transmitted and absorbed solar energy that enters into the building's interior. The higher the SHGC the higher the heat gain.

Solar Reflective Coatings:

Coatings that reduce heat gain through higher solar reflection.


A desiccant filled frame used to separate two lites of glass in an insulating unit.


The panel(s) of a wall located between vision areas of windows which conceal structural columns floors and shear walls.


A measure of heat gain or heat loss through glass due to the thermal conductance and the difference in indoor and outdoor temperatures. As the u-value decreases, so does the amount of heat that is transferred through the glazing material. The lower the u-value the more restrictive the fenestration product is to heat transfer; reciprocal of r-value.

Warm Edge:

Term used to describe insulating spacer technologies that achieve better center of glass thermal performance (u-value) than a traditional aluminum spacer.

Glass Panes


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