Glass Related Glossary

glass glossary

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  AAMA (American Architectural Manufacturers Association): A national trade association that provides suggested standards within industries dealing with windows, doors, curtain walls, skylights, and storefronts.
  Abrasion: Abrasion creates shallow decorations by grinding them with a wheel which leaves them with an unpolished finish.
  Acid Etching: Hydrofluoric acid is applied to decorate the surface of the glass, creating a similar look to weathering. For weathering, glass is exposed to the acid’s fumes for a matte surface.
  Acid Polishing: It creates a polished surface on cut glass, dipped into a mix of sulfuric and hydrofluoric acids.
  Acid Stamping: A rubber stamp-like tool is used to put a trademark onto the annealed glass.
  Adhesion: The measure of a coating or sealant’s ability to stick to any surface.
  Adjustment Clip: Used to align jambs after window installation, adjustment clips are hung onto window jambs.
  Air Infiltration: The air which leaks in and out of cracks in walls, windows, or doors in a building
  Ambient Temperature: The outside temperature.
  American Value: 1W/ k = 0.176 Btu/sq.ft./F/h
  Annealed Glass: This type of glass is created in molten form in a long oven. The glass is heated and cooled, resulting in a flat sheet of glass. If this type of glass does break, it creates long and sharp shards.
  Annealing: Slowly cooling a glass object to reduce the stresses associated with rapid cooling. It reduces the chance of the glass item breaking at a later time.
  Annealing Oven: Allows a molten glass object to cool slowly, reducing the change of breakage.
  Anodize: Creating a hard oxide film on the surface of aluminum as a result of electrolytic action.
  ANSI (American National Standards Institute): An organization that deals with standards and specifications for products.
  Argon: A nontoxic gas that is used to increase insulation and is injected into IGU.
  Arched windows: These windows have rounded tops and are often installed above standard windows. They usually don’t open and close.
  ASHRAE: American Society of Heating, Air-conditioning, and Refrigeration Engineers.
  Aspect Ratio: The ratio of a panel comparing its longer and shorter sides.
  ASTM (American Society for Testing and Material): This organization creates material standards and test methods. They have also introduced a window installation standard.
  Awning Window – This type of window has a sash swinging out from the bottom.


  Balustrade: This low wall type creates a parapet to anywhere with a change in levels, such as a stair or balcony.
  Bay windows: Bay windows stick out from an exterior wall, forming a small shelf. These use flat windows in an angle frame, which are built out from the property.
  Base Wall: This is a short wall that is found below the glazing of exterior walls.
  Bead: A bead is molding which is placed around a window frame to ensure the glass is held in place by pressure.
  Bent Glass: A piece of flat glass is heated to its softening point and can then be shaped into a curve when hot.
  Bevelling: Edge finishing a piece of flat glass to a bevel angle.
  Bow Window: A bow window is a composite of at least four window units in a bow formation, which has a gentle curve to its appearance.
  BTU: British Thermal Unit. This measurement is the amount of heat required to increase the temperature of 1lb of water by one degree Fahrenheit.
  Bullet Resistant Glass: This glass option is strong enough to stop firearm attacks or bullets breaking through it.
  Butyl: Used as a sealant or glazing tape, this is a synthetic rubber. It’s created by the co-polymerization of isobutylene with the addition of a little bit of isoprene.


  Carving: Using a hand-held tool or sand blasting to remove the glass from an object’s surface.
  Ceramic Printed Glass: Sometimes called ceramic fritted glass. This type of glass is created by applying ceramic or glass frit before the thermal tempering process.
  Casement Window: Usually opens like a door. This type of window has hinges on its side.
  Casing: This type of molding comes in different widths, shapes, and thicknesses and is applied to the framework of windows and doors. Interior casing is a flat type of decorative molding which covers the inside edge of the jambs and the opening between the window unit and the wall, and exterior casing offers the same benefits.
  Casting: The ways to make glass in mold, which can include sand or kiln casting.
  Center of Glass: This is the central part of a window and excludes the 2.5 inches nearest the edge. It’s used for calculating certain indicators such as the U-value and R-value.
  CFM (Cubic Feet per Minute) – A measurement that is used in air infiltration testing.
  Channel: A U-shaped opening with three sides that’s used to receive a lite or panel.
  Channel Glazing: The process of sealing the joints around glass lite or a panel set in a U-shaped channel.
  Check Rail: You’ll find this on a double-hung window, where the top rail of the bottom sash and the base rail of the top sash has the lock mounted. They should meet when the window is closed.
  Chemically Tempered Glass: Instead of using thermal processing, glass is tempered by chemical reaction.
  Chord: The lines in a piece of clear glass with a slightly different expansion coefficient that all refract the light at varying rates.
  Chunked: A badly damaged piece of glass.
  Cladding: On the exterior of frame and sash components, this is the type of material that will be placed.
  Color Properties: This refers to the color of the glass when you are looking through it straight-on or at a 10-degree angle from normal. It’s shown using the 3-dimensional CIE L*a*b* color space.
  Color Rendering Index (CRI): Measured on a scale of 1 to 100, this is the ability to portray colors through the glazing in comparison to those seen in daylight.
  Comfort Engineering: Selecting and adjusting windows one by one to fit the desired budget, aesthetic, and comfort level.
  Compatibility: When two or more materials are working together without any issues, for an extended period.
  Condensation: When warm air comes into contact with a cold surface, water converts from vapor to liquid due to an increase in temperature. 
  Conduction: When heat moves through a material by molecular agitation, this process of heat transfer takes place.
  Conductivity: The transfer of heat through a specific material.
  Convection: A heat transfer process that involves motion in a fluid that comes about as a result of the difference in density of the fluid and gravity.
  Corridor: A passage or space of circulation.
  CRF (Condensation Resistance Factor): Indicates how well a window can resist condensation, based on AMMA standards. 
  Curtain Wall: A partition of glass that’s attached in a frame or a non-load bearing structure.


  Dade County: A county located in Florida, which includes Miami. It has many additional standards for hurricane-resistant windows and doors.
  Daylight Transmittance: The amount of visible light that glazing allows through a window. A standard clear dual-pane allows 82%.
  Decibel: A unit that shows the intensity of sounds on a scale. It is ranging from zero to 130 for the average pain level.
  Decorative Glass: Vision glass or spandrel glass is either silk-screened, painted, sand-blasted, or acid-etched to create any desired effect or design.
  Desiccant: A crystalline substance which is used to absorb moisture or sealant solvents, within the sealed air space of IGU.
  Design Pressure: The wind load of a project, which is determined by the architect and expressed in psf.
  Designation Number: As recommended by AAMA and there is one for each window style.
  Dew Point: The temperature that water vapor will condense to become warm air.
  Direct Energy Transmission (DET): The percentage of solar energy flux transmitted through glass with a density of between 300 and 2150 nm.
  Direct Gain: This type of passive solar system uses south-facing windows to give a building more sun exposure.
  Double Glazing: Two panes of glass are used within a window. Offers increased energy efficiency and other benefits.
  Double Glazing Panel (DGP): An interior glass panel that’s removable and creates an air space in between the exterior glazing and the DGP. This offers better insulation and condensation control and enables between-glass shading.
  Double Strength Glass (DSG): 1/8″ thickness.
  Double-Hung Window: A unit with two operable sashes on the windows, which will vertically bypass each other within one frame.
  Dry Glazing: Secures glass in a window frame with a dry and preformed gasket. This process does not involve a glazing compound.
  Dual Durometer: A material with two or more flexibility levels
  Dual Glazed: Two single lites which are glazed into a split sash that includes an airspace. It’s not hermetically sealed in between the two single lites.
  Dual Window: Two windows which are joined together to offer improved control of sound. They are placed one in front of the other.
  Dual Pane: Two panes of glass that just have a single airspace. They are held together with an edge spacer and are the most economical type of Insulated glazing unit (IGU).


  Edging: Grinding flat glass to create a specific shape or size edge.
  Egress Window: A window that has specific release hardware and a minimum clear opening size. It acts as an emergency fire escape.
  Elasticity: Another word for pliability. This discusses the ability to expand and contract.
  Emissivity: The ability to radiate heat as long-wave radiation.
  Enameling: Painting and baking glass.
  Energy Absorption (EA): The percentage of solar energy flux which is absorbed by the pane in a glazed wall. This energy is then reradiated at different rates either inside or outside depending on the glass itself and other external elements such as the temperature and wind and air speed.
  Engraving: Cutting the surface of annealed glass. This process is completed by holding it on a rotating abrasive wheel, or it can be scratched with a diamond.
  ER Rating: Developed by CSA (Canadian Standards Association). It’s measured in watts per square meter (W/m2), and is designed to compare the thermal performance of windows. 
  Expansion Mullion: Self-mulling window frame jambs. When they are slipped together they preserve strength and water tightness yet still permit contraction and expansion.
  Exposed Edge: A glass edge that is visible and uncovered after glazing.
  Extension Jambs: Extension jambs are flat wood parts that are nailed to the interior edges of the window jamb. This allows it to extend in width to adapt to a thicker wall. They are flush with the wall surface, and the interior casing will then be nailed in.
  Exterior Glazed: Glass which is glazed from the building’s exterior.
  Extra Clear Glass: Float glass that is purer and has a lower iron content. It offers improved transparency, however doesn’t have the green tint of normal float glass.
  Extrusion: When heated material is forced through a die and is used to produce aluminum, vinyl (PVC) and other components.


  Façade: The front or the face of a building.
  Fading Factor: Reduce fading or damage to interior fabrics with this glazing option.
  Fenestration: The way openings of a building are designed to help let light in.
  Fin: A piece of glass which provides lateral support thanks to its position and fastening.
  Fin Seal: A pile of weatherstrip with a plastic mylar fin in the center. This helps to reduce air infiltration, and the weatherstrip will experience contact throughout the life of the window.
  Fire Resistant Glass: A piece of glass that’s designed to stay in place without flames, gases, and smokes passing through for 30, 60, 90, or 120 minutes to allow homeowners to evacuate safely.
  Fixed Lite: Non-operable or non-venting window.
  Fixed Panel: Non-operable panel, which is commonly combined with operable door units.
  Fixed Window: A non-operable window.
  Flashing: A type of metal that’s used to prevent water penetration and offer water drainage. It’s often used between a roof and wall and over exterior windows and door openings.
  Flat Glass: A term used for sheet glass, float glass, and some rolled and plate glass.
  Float Glass: Transparent glass with a flat and parallel surface. It’s formed on the top of a pool of molten tin.
  Foam Spacer: A piece of foam material that’s placed in the airspace of insulating glass windows. They work to improve the appearance and performance of a window.
  Fogging: Contamination that’s left on the inside surface of the sealed IGU. This is a result of extreme temperatures.
  Frame: Outside parts of a window unit that enclose the sashes. The frame is made up of a head jamb, side jambs, and a sill.
  Frameless Glazing: A glazing surface which doesn’t have a visible frame and that is held together by patch fittings, spiders, or bolts.
  French Door: A set of hinged doors which open up from the middle.
  French Sliding Door: A sliding door that has wider panel members surrounding the glass. This helps to give it the look of a French hinged door.
  Front Wall: Wall of a structure between the two gable end that runs the length of a building. 
  Fully Framed Glazing: Panels that have all of their edges framed.


  Garden Windows: Mini bay windows designed for plants. 
  Gas-filled Glass: A gas (not air) that’s put between insulated glass to reduce the U-factor. It works to suppress conduction and convection, and the most commonly used gases are krypton, argon, and carbon dioxide.
  Gasket: A pliable rubber or plastic material that’s used to separate glazed glass and aluminum/vinyl.
  Glass block windows: These are a type of accent and offer increased light flow to a section of your home.
  Glazing: The polycarbonate or glass panes in a structure. This is also used to describe the act of installing panels of glass.
  Glazing Bead: A molding around a window frame. It applies pressure to the glass and will help hold it in place.
  Glazing Stop: The section of the sash or door panel holding the glass in its place.
  Green Building: A movement aimed to create occupant and environmentally friendly buildings and structures. Areas that are looked at include energy efficiency, sustainability, and health.
  Greenhouse Effect: Property of glass that permits short-wave solar radiation transmission, which is still opaque to long-wave thermal radiation.


  Heat Soak or Heat Soaking: A process completed on the toughened glass where it’s reheated to a temperature of 290°C. It’s kept at this temperature for eight hours and then will be left to cool slowly.
  Heat-Strengthened Glass: This process heats glass up to 1300º F, then rapidly cools the glass with air. It’s a similar process to the one used for tempered glazing and results in the thermally-strengthened glass. This type of glass is two times the strength of annealed glass, and there is less chance of breakage.
  Heat Gain: Heat transfer from the outside of a window to the inside. Heat gain is measured by the fuel consumption that’s required for a comfortable indoor temperature.
  Heat Loss: The heat transfer process from the inside of a window to the outside. This process involves convection, conduction, and radiation.
  Heat Treating: Glass or aluminum extrusions are heated and cooled. This results in the material becoming stronger and harder.
  Hermetically Sealed Unit: An IGU that is sealed to protect it from moisture. Two lites of glass are separated by a roll-formed metal spacer tube which contains a moisture-absorbing material. It’s then sealed, which stops moisture from getting into the air space.
  Hopper windows: This type of window opens from the top and is usually cranked to tip the windows down and open. They are ideal for small spaces.
  Hurricane Impact Resistant Glazing: In coastal regions that are at risk of hurricane winds and debris. Certain laminated glass products can meet these requirements, and they are tested to ensure they’ll withstand the forces of these natural disasters.


  ICC (International Code Council): A national organization. The ICC publishes codes for states and agencies to use, including the International Building Code (IBC) and the International Energy Conservation Code (IECC).
  IGCC (Insulating Glass Certification Council): A certification program of accelerated lab testing and unannounced plant inspections. This ensures glass performance conforms with ASTM E 774-88.
  Impact-resistant: Windows and doors that have passed tests for resistance to wind-borne debris. Ideal for use in hurricane-prone coastal regions.
  Infiltration: The seepage of air into a room through cracks around windows and doors.
  Infrared (long-wave energy): This energy is generated by radiated heat sources. These include electric coil heaters or natural gas-powered, forced-air furnaces. This energy is produced by any object that can absorb heat and radiate it.
  Insolation: Incident solar radiation. This is the total radiation hitting an exposed surface.
  Insulated Glass (IG): IG glass is made up of two pieces of glass with an airspace interlayer. This helps to protect a room from the outdoor temperature. 
  Insulation: A material with high resistance (high R-value/low U-value). It’s used to retard heat flow.
  Integral Mullion: A kind of frame that’s trapped within the master frame. It’s used to separate fixed glass or vents.
  Interior Glazed: Glass glazed from the inside of a building.
  Internal Gain: The heat generated in the interior of a building, from lights and appliances.


  Jalousie windows: A unique window style that features multiple slats of metal or glass and opens up like blinds.


  Laminated Glass: It is made of a polyvinyl butyral, a plastic interlayer material, keeping the glass in place if it does happen to bread. Even after impact, the glass will remain within the frame, and it’s a type of safety glazing that can be used with various glass options for its layers.
  Lehr: A computer-controlled kiln to create annealed glass.
  Light Reflection (LR): The ratio of the light flux reflected by the glass against the incident light flux shown by the illuminant CIE D65.
  Light-to-solar gain ratio: The ratio of visible light to solar heat gain. LSG=VLT/SHGC. A higher number offers improved solar control.
  Light Transmission (LT): Ratio of light flux transmitted through the glass to the incident light flux and shown by the illuminant CIE D65 with a spectral density of between 380 and 780 nm.
  Lite: A term used to describe a pane of glass, a window, or a compartment of a window. It can also be spelled “light.”
  Low Iron Glass: This type of glass has only about 10% of the iron content of the glass. It offers 90% light transmission and reduces the greening effect of thicker glass.
  Louver: A slatted opening that provides ventilation. At the same time, it will stop rain from entering the home.
  LowE Coating: It is a very thin, almost invisible metal layer that are placed on a glazing surface. They reduce the U-factor as they suppress radioactive heat flow.


  Mill Finish: Unfinished and unpainted aluminum.
  Mirror: A piece of glass that is silvered on one side and has a protective paint coating.
  Mock-up: It is part of a wall that can either be built full size or scale. It’s used for testing and studying before construction begins.
  Moisture Vapor Transmission Rate: The rate that moisture diffuses through a substance. It was shown in the unit grams/meters2 x 24 hours. A lower rate is more desirable to avoid moisture. 
  Mold: Made from clay, wood, or metal and used to shape glass.
  Monolithic Glass: It is a numeric designation that indicates the thickness of glass.
  Mosaic Glass: Glass objects which are made from pre-formed elements, that are then put in a mold and heated until they are fused.
  Mullion: A horizontal or vertical member to support and hold panels, sash, glass, or part of a curtain wall.


  OITC: Outdoor-Indoor Transmission Class (OITC) measures the amount of outside noise that will make it through a window.


  Pane: A piece of flat sheet glass that is used for window glazing.
  Patterned Glass: Glass that has a pattern on one or both of its sides. This can be used for light control, baths, and decoration. It may also be referred to as obscure, figured, or rolled glass.
  Palladian Window: A large, arch-top window that’s surrounded by smaller windows on either side.
  Pane: It is a framed sheet of glass.
  Patio Doors: Sliding glass doors that usually lead out to the deck or terrace of a home.
  Permeability: The amount of permitted passing water through an opening before it causes rupture.
  Picture Window: A large stationary window that’s designed to offer the best views.
  Polycarbonate: Strong and semi-transparent plastic that’s used instead of glass. It’s cheaper than glass and comes in a variety of thicknesses.
  Polymerization: A reaction that occurs when two or more molecules of a compound unite to create a larger compound.
  Polysulfide: Polysulfide liquid polymers are long-chain aliphatic polymers that contain disulfide linkages. At room temperatures, than can be converted to rubber without any shrinkage after a curing agent is added.
  Projected Window: A window in which opens on hinges or pivots. It usually refers to casement and awning windows.
  PSF (Pounds Per Square Foot): An air pressure measurement used in window testing
  PSI (Pounds Per Square Inch): An air pressure measurement used in window testing
  PVC (Polyvinylchloride): An extruded material that’s used on windows and door frames.
  Pyrolytic Coating: A special coating that is applied directly onto the glass while in its molten state. This results in a permanent surface coating.


  Radiation: It is the transmission of heat through space. This process works by means of electromagnetic waves or particles with transfer from one surface to another.
  Rail: The bottom and top members of the framework of a door panel or a window sash.
  Reflectance Back: A measurement (expressed in a percentage) of the visible light reflected into a room. External visibility is higher with a lower rating.
  Reflective Coated Glass: Glass with a metallic or metallic oxide coating that’s applied onto or into the glass surface. It provides a reduction of solar radiant energy, conductive heat energy, and visible light transmission.
  Reflected Radiation: The solar radiation that hits an exposed surface after being reflected from the ground or other structures.
  Reflective Glass: A kind of glass with a metallic coating. It helps to reduce solar heat gain.
  Relative Heat Gain: A measurement of the total heat gain through the glazing with a set of conditions.
  Relative Humidity: Humidity (shown as a percentage) of the maximum possible humidity at a specific temperature.
  Roller Wave: The sporadic wave imparted to glass during heat treatment. It’s measured by the peak-to-valley distance.
  Round Circle windows: Round, half-round, oval, or elliptical-shaped windows that add decoration to your home.
  R-value: The resistance to heat gain or loss. A higher R-value indicates greater resistance to heat flow and insulating value. This is the inverse of the U-value.


  Safety Glass: It is a kind of heat-treated glass that is less likely to break or splinter.
  Sandblasting: A way of creating a matte finish by bombarding glass with fine grains of sand. These are propelled by compressed air, and each layer that removes results in a cloudy dull finish result with every layer removed. 
  Sand Casting, Sand Molding: Molten glass is poured into a mold of compacted sand. A granular surface appears as the result of glass coming into contact with the sand.
  Sash: The framework that holds the glass in a window unit. It’s made up of stiles on the sides and rails on the top and bottom.
  Sash Cord: A chain or rope which attaches the sash to the counterbalance in double-hung windows.
  Sash Lift: On a double-hung window, it’s a handle that’s screwed to the inside bottom rail of the lower sash.
  Satin Glass: A type of glass with a matte finish or frosting.
  Sealant: A compressible plastic material that’s to seal any opening, such as between the glass and a metal sash. It’s usually made from silicone, butyl tape, or polysulfide.
  Security Glass: A laminated glass that’s designed to prevent forced entry. Best used on large pieces of glass in windows without safety grills.
  Seismic Load: The force produced on a structure during an earthquake.
  Self-cleaning Glass: Glass treated with a coating that uses the sun’s UV rays to create a photocatalytic effect that breaks down organic dirt.
  Shading Coefficient (SC): The total solar energy passes through a glass relative to a 1/8″ (3 mm) thick clear glass.
  Shower doors, shower screens, and bath enclosure: These are the panels and windows used to enclose a shower or bath.
  Silica: Silicon dioxide. It is a mineral that’s the main ingredient in glass, and the most commonly used option is sand.
  Sill: The lowest member in a door or window that sits horizontally. It’s usually slanted down and to the outside to shed standing water.
  Silicon: A type of sealant that’s used during glazing.
  Simulated Divided Lites (SDLs): Glass that has the appearance of a number of smaller panes. It’s actually a larger glazing unit that has muntins placed between the layers.
  Single Glazing: A single layer of glazing that encloses a structure, which is usually glass or plastic.
  Single Hung Windows: The lower window panel or sash moves up and down with this type of window, and the upper sash remains stationary.
  Skylight: A fenestration surface with a slope of less than 60° from the horizontal plane. Without this slope, it would be considered vertical fenestration.
  Skylight Windows: A way to add additional light into a room when you are short of space.
  Sliding Door: A vent panel moves horizontally on a track system past a fixed panel with this type of door.
  Sliding windows: They have two sections that are made from single windows. One section slides over the other horizontally to open and close.
  Sloped Glazing: A glass installation that is at a slope of 15 degrees or higher from vertical.
  Slumping: The reheating of a blank until it’s soft and flows into a former mold. It eventually takes the shape of the mold, and this process is sometimes called sagging.
  Solar Heat Gain Coefficient (SHGC): A new term that measures the amount of solar energy gained through a window. When you multiply this by 100, it will give you the percentage of solar energy that a building allows in.
  Spandrel: The portion of an exterior wall in a multistorey commercial building that covers the area below the sill of a vision glass installation.
  Soda-lime Glass: The most common form of glass which contains three major compounds in varying proportions. These are usually silica, soda, and lime.
  Solar Control Glass: This glass option is used to reduce the effect of heat transfer from solar radiation into a home or building.
  Solar Heat Gain Coefficient (SHGC): The solar heat gain coefficient (sometimes called a shading coefficient) measures how efficiently a window absorbs and reflects heat. In an area with a hot climate, look for a lower number.
  Sound Transmission Class (STC) Rating: This rating measures the amount of noise reduction that can be achieved with a product.
  Spacer: The spacer in IGUs is at the perimeter. It keeps the two lites of glass separated at a specific width. The spacer can be made from aluminum, stainless steel, silicone foam, and other materials.
  Spontaneous Breakage: Tempered glass breakage happens without any provocation or external reason.
  Sputtering: A metal coating process used on glass surfaces.
  Stained Glass: Decorative windows are made of pieces of colored glass. They are fitted into cames and then set in iron frames. Alternatively, stained glass can be colored throughout by metallic oxide, flashing, or decorated with enamel.
  Staining: Coloring the surface of a piece of glass with silver sulfide or silver chloride. This is then fired at a low temperature. It leaves a yellow, brown-yellow, or ruby stain, which can then be painted, etched, or engraved.
  Storm windows: Exterior windows that are installed in the same frame as your current windows. They will block out drafts and reduce heat loss and are ideal for cold or inclement weather.


  Tempered Glass: Glass that is created by heating annealed float glass up to its softening point (1300º F). It’s then quickly cooled with air. This results in glass that’s four to five times stronger than regular annealed glass and will break into small particles if shattered.
  Thermal Barrier: A stop of non-conducting material, such as vinyl, wood, or foam rubber. It’s used to separate the inside and outside surfaces in a metal frame. This reduces the conduction of heat to the outside, resulting in a cold inside surface.
  Thermal Break: A low conductance element placed between higher conductance elements to reduce heat flow. It’s regularly used in aluminum windows.
  Tilt-turn windows: Offers two operation types in one unit—a simple handle movement or turning the handle.
  Tinted Glass: A type of glass with a specific color. It also offers light and heat-reducing capabilities.
  Toughened Glass: Also called tempered glass. It’s made by heating annealed float glass to its softening point (1300º F), then quickly cooling it with compressed air.
  Transom windows: Decorative accent windows that break up a space and offer a decorative element.
  Transmittance: The chance of the glass passing light or heat. It’s usually expressed as a percentage.
  Triple Glazed Units: It is an insulated glass unit, that uses three plates of glass that are separated by two air gaps.


  uPVC: Unplasticized polyvinyl chloride. This is a rigid and chemically resistant form of PVC, which is often used for piping and window frames.
  U-Factor: The U-factor measures the insulation value of the whole window. The lower the figure, the better the insulation value.
  U-Value: Measures the insulating characteristics and how much heat gain or loss occurs through the glass as a result of the difference between indoor and outdoor temperatures. A lower figure is more desirable, and the U-value is the reciprocal of the R-value.
  Ultraviolet Light (UV): Rays of solar radiation that are invisible and are at the short-wavelength violet end of the spectrum. These can cause fading in homes on painted surfaces, materials, and carpets. 


  Vent Unit: A window unit that opens and closes.
  Visible Light Transmittance (VLT): The percentage of the visible light striking the glass that then penetrates to the inside of the room. It’s shown as a number between 0 and 1.
  Visible Light Reflectance (VLR): The percentage of visible light that is reflected out by a glazing system. It’s shown as a number between 0 and 1.


  Weatherstrip: A material that’s used to seal the openings or gaps in venting windows. It works to reduce air and water infiltration.
  Wet Glazing: This method secures the glass in a frame with a glazing compound or sealant.
  Wind load: The force of the wind against an exposed surface of a building. It is shown in pounds per square foot (psf).
  Window Sill: A solid wall that starts from the finished floor level and goes to the base of the first window.
  Wired Glass: This is a type of rolled glass with a layer of meshed wire embedded inside it. You can find this as polished glass and patterned glass. The wire stops fragments of glass from falling out of the frame when it’s broken.
  Window Wall: A commercial metal curtain wall where the windows are the most prominent element. It can also be used to describe the smallest fixed lites used within wall systems.

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