Glossary of Terms for Glass and Glazing
Available in Annealed (non-toughened) and Toughened Safety Glass.

Acoustic Glass

Glass designed to reduce noise transmission, typically by combining multiple layers of glass with sound-dampening interlayers. This makes it ideal for environments requiring noise control, such as homes near busy streets, offices, or schools. The greater the thickness and the number of layers, the better the soundproofing properties.

Air Gap

The space between the panes of glass in double-glazed or triple-glazed units, which acts as a barrier to heat transfer. The width of the air gap can significantly affect the thermal efficiency of a window or unit. The larger the gap (within certain limits), the better the insulation properties, as it slows the transfer of heat between the inner and outer surfaces of the glass.

Annealed Glass

Standard, untampered glass that is cooled slowly after manufacturing to reduce internal stresses. It’s the most basic form of glass and can be cut, shaped, and polished easily. However, it can break into sharp shards upon impact. It’s commonly used for windows and glass doors that are not subject to heavy impact or safety requirements.

Antisun (Bronze/Grey)

Tinted glass reduces glare and solar heat gain, making it ideal for buildings with high sun exposure. It also enhances aesthetics and privacy. It provides solar control and glare reduction while adding a stylish appearance to windows. Perfect for warm climates and large glazed facades.

Argon Gas

A colourless, odourless, inert gas used between the panes of double and triple-glazed units. Argon helps to enhance insulation by reducing heat transfer, as it has a lower thermal conductivity than air. This helps improve the overall energy efficiency of sealed units, reducing heating and cooling costs in buildings.

Bespoke Glass

Custom-made glass units designed to meet specific measurements, shapes, and aesthetic requirements. Whether it's a unique window size, a custom color or pattern, or an unusual shape, bespoke glass ensures that the final product fits perfectly into your design. It is often used in residential and commercial projects where standard sizes are not suitable.

Beading

The strips or mouldings used to secure the glass unit within a window frame or door frame. Beading is essential for holding the glass securely in place and preventing movement. It also helps provide a finished, aesthetic appearance by concealing the edges of the glass.

Blown Unit

A term used to describe a failed sealed unit where moisture or condensation has infiltrated the gap between the glass panes. Blown units are typically characterized by fogging, misting, or cloudy appearance that can’t be wiped away, as the moisture is trapped within the sealed unit. They often require replacement to restore the window’s thermal performance and clarity.

Butyl Sealant

A synthetic rubber-based sealant that is used as a primary adhesive to seal the edges of double or triple-glazed units. Butyl is known for its excellent waterproofing and insulating properties, as well as its flexibility, which allows the unit to accommodate slight movements without breaking the seal.

Cavity Width

The distance between the two or three panes of glass in a double-glazed or triple-glazed sealed unit. The cavity is typically filled with an inert gas such as Argon to improve thermal insulation. The width of the cavity directly impacts the thermal performance of the sealed unit, with a wider cavity generally providing better insulation.

Condensation

The process of moisture forming on the surface of glass due to temperature differences between the interior and exterior of a building. In sealed units, condensation can be a sign that the unit has failed, and moisture has entered the air gap. While condensation on the outer surface is normal, condensation between the panes indicates a broken seal or blown unit.

Curved Units

Double-glazed units designed to fit curved or arched frames. The glass is bent to create a smooth curve, offering aesthetic appeal while maintaining the insulating properties of standard double glazing.

Desiccant

A moisture-absorbing material used in the spacer bar of sealed units. Desiccants are critical in preventing condensation inside sealed units by keeping the air gap dry and free from moisture. Without desiccant, the seal between the panes could fail, leading to a blown unit and reduced insulation properties.

DGU (Double Glazed Unit)

A generic term used to refer to a double-glazed sealed unit, where two panes of glass are sealed together with a spacer bar, creating a cavity filled with an insulating gas. Double-glazed units are the standard in energy-efficient windows and doors, improving thermal insulation, reducing noise, and enhancing security.

Drawn Glass

Drawn glass is produced by drawing molten glass into sheets, typically used for windows and other clear glazing applications.

Duplex Bars also known as Back to Back or Spacer Grid

A type of glazing unit that features internal spacers and external stick-on astragal bars. The internal spacer is used to separate the panes of glass, while the external bars are adhered to the outside of the glass to create the appearance of separate panes, providing a traditional or decorative look. This design combines the benefits of modern double glazing with the aesthetic of divided lights.

Energy Efficient Glass

Glass designed to minimize heat loss and maximize energy savings. This is achieved using coatings like Low-E, which reflect infrared light back into the building, keeping heat inside during the winter and outside during the summer. Energy-efficient glass also contributes to better indoor comfort and reduced reliance on heating and cooling systems.

Float Glass

A type of glass made by floating molten glass on a bed of molten tin to create a perfectly flat surface. This is the most common type of glass used for windows and glazing in buildings. It’s available in various thicknesses and can be cut or treated to meet specific requirements.

Frosted Glass

Glass that has been treated (typically by sandblasting, acid etching, or applying a film) to create a translucent, textured surface that obscures vision. Frosted glass is commonly used in bathrooms, office partitions, and other applications where privacy is desired without sacrificing natural light.

Glass

Glass is a transparent or translucent material made from silica, soda, and lime, which can be formed into various shapes and thicknesses for a wide range of applications.

Glass Fabrication also known as Processed Glass

Glass fabrication involves cutting, shaping, and finishing glass to meet specific design requirements for a variety of applications, from windows to custom glass products.

Glazing

Glazing refers to the installation of glass into frames or other structures, providing transparency, protection, and aesthetic properties to buildings and vehicles.

Glazing Mastic

Glazing mastic is a type of sealant used to secure glass in frames and provide a weather-tight seal, often applied in a caulk-like form.

Insulated Glass Unit (IGU)

An insulated glass unit is a sealed assembly of two or more glass panes separated by a spacer and filled with gas, offering improved thermal insulation and energy efficiency.

K-Glass

A brand name for Low-E glass that incorporates a special coating designed to reflect infrared light and reduce heat transfer. K-glass is typically used in energy-efficient windows and building facades to improve thermal insulation and reduce the need for heating and cooling.

Kitemark

A certification mark issued by the British Standards Institution (BSI), indicating that a product meets specific quality and safety standards. The Kitemark is often found on products like windows, doors, and building materials, ensuring they have been rigorously tested for performance, durability, and compliance with industry regulations.

Krypton Gas

A noble gas used in high-performance sealed units, often as an alternative to Argon. Krypton has lower thermal conductivity, which makes it a more efficient insulator, particularly in windows that need to offer superior energy efficiency. It is often used in triple-glazed units and premium window systems.

Laminated Glass

A type of safety glass made by bonding two or more layers of glass with a plastic or resin interlayer, typically polyvinyl butyral (PVB) for domestic use. The layers are fused together by heating. Laminated glass is primarily used for security and safety purposes. Its interlayer is difficult to pierce, and it remains intact when broken, with the glass staying bonded to the interlayer. This makes it ideal for applications such as skylights, glass ceilings, car windshields, and aircraft cockpits, where it prevents shards from falling or causing injury. Laminated glass is also tested for its ability to withstand manual attacks, including using tools like an axe.

Leads

Thin strips of metal, typically lead, used in glazing to create decorative patterns or divisions in glass panels. In double-glazed units, leads can be used to simulate the appearance of smaller panes of glass, much like Georgian bars or Duplex bars. Leads are often incorporated into stained glass or decorative glazing, where they help to outline or frame individual sections of the glass. In modern glazing, leaded lights are often used for aesthetic purposes while still maintaining the insulating properties of double glazing. The metal leads are either embedded between the panes in sealed units or applied to the surface of the glass. While traditional leads were made from lead, modern alternatives such as zinc, aluminium, or steel are often used for durability and safety reasons.

Low Profile Units also known as Heritage or SlimLine

Double-glazed units that use a 4mm or 6mm spacer bar, resulting in a lower sightline compared to standard spacer bars, which are typically thicker. These units are particularly useful for windows with narrow glazing rebates, where a standard spacer bar would be too visible or would not fit properly. Low profile units are special order items, sourced from suppliers, and are available in three colours for the spacer bar:

• Silver
• Black
• White

Low-E Glass (Low Emissivity Glass)

Glass coated with a microscopic layer of metal oxide that reflects heat while allowing visible light to pass through. The coating helps minimize the amount of infrared and UV light passing through the glass, enhancing the window's energy efficiency. Low-E glass is widely used in double-glazed and triple-glazed units to improve insulation and reduce heating/cooling costs.

Metal Spacer Bar

A spacer bar made from metal, typically aluminium, used between the glass panes in sealed units. While aluminium offers durability and strength, it is less efficient than warmer materials such as foam or stainless steel in terms of insulation. Metal spacer bars are often used in traditional glazing systems.

Misted Unit

A sealed glass unit that has developed condensation or mist between the panes, often indicating that the seal has failed and moisture has entered the unit. Misted units are considered damaged and generally need to be replaced to restore the unit’s insulation and appearance.

Modified Glass

Glass that has undergone special treatments or coatings to alter its properties, such as thermal insulation, UV protection, or colour. Tempered glass, laminated glass, and Low-E glass are examples of modified glass products designed for specific applications.

Noise Reduction Glass

Glass specifically designed to reduce sound transmission. It is typically made by combining layers of glass with interlayers of sound-dampening materials like PVB or EVA. This type of glass is ideal for environments that require quiet, such as residential areas near highways, offices, or hotels.

Non-Reflective Glass

Glass that has been treated or coated to minimize the amount of light or image reflection on its surface. This type of glass is commonly used in applications where visual clarity is essential, such as in display windows or museum environments, and it helps reduce glare and enhance the viewing experience.

Obscure Glass also knows as Pattern or Privacy Glass

A type of glass that has been treated or patterned to obscure visibility while still allowing light to pass through. It is commonly used in areas where privacy is needed, such as bathroom windows, shower doors, or office partitions. The glass can be made obscure through methods like frosting, texturing, or acid etching. This makes it ideal for spaces where light transmission is desired but clear visibility is not.

Patterned Glass

A type of glass that has a decorative texture or pattern applied to its surface. This type of glass is often used for privacy or aesthetic purposes, as the patterns distort the view through the glass while still allowing light to pass through. Patterned glass can be made using various techniques, such as embossing, rolling, or pressing the pattern into the glass during its production. Common applications include bathroom windows, shower doors, internal partitions, and decorative windows. Read more...

Planitherm 1.0

This is a high-performance soft coat Low-E (low emissivity) glass designed to enhance thermal insulation in double and triple-glazed units. It features an advanced low-emissivity coating that helps to minimize heat loss, improve energy efficiency, and provide superior comfort in residential and commercial glazing applications.

Polycarbonate Glass

A type of plastic that is often used as a lightweight alternative to glass. Polycarbonate has excellent impact resistance, making it ideal for applications where glass is at risk of being broken. It is used in areas requiring high-security or safety features, such as in windows, skylights, and partitions.

Privacy Glass

Glass that can be switched between transparent and opaque to provide privacy on demand. Privacy glass is commonly used in office partitions, bathrooms, and other areas where privacy is important but natural light is still desired. It typically uses smart technology such as electrochromic or liquid crystal displays to control opacity.

Raked Units

Double-glazed units with a slanted or angled edge, often used in rooflights or skylights where the glazing needs to follow a slope or pitch. The rake refers to the angle or incline of the glass, and the unit is designed to fit seamlessly into sloped areas of a building, providing both light and insulation while maintaining a secure fit. Raked units are typically custom-made to match the specific angle of the roof or structure they are intended for.

Reach Around Callipers also known as Wrap Around Calipers

A type of measuring tool used in the glazing industry to measure the rebate or gap within window frames. These callipers are designed with adjustable arms that can reach around the frame, allowing for precise measurement of internal dimensions. They are especially useful for measuring tight or difficult-to-access areas and ensuring the correct fit for glazing units.

Rebate Depth

Typically, between 20mm to 25mm, this depth is designed to accommodate the thickness of the glazing unit along with the necessary space for glazing tape or seals.

Rebate Measurement

When measuring for a window rebate (tight sizes), adjustments are made based on the type of frame.

For uPVC frames, you need to deduct 10mm from both the width and height.

For wooden frames, you need to deduct 6mm from both the width and height.

These deductions account for the space needed for fitting the window into the frame.

Tolerance for Installation also known as Wiggle Room

When measuring for a window rebate (tight sizes), it is crucial to allow tolerance to account for slight expansion or contraction of the frame due to changes in temperature and seasons. Without this flexibility, the glass may crack under pressure. Additionally, installation products, such as packers, putty on a roll, and other materials, should be factored into the measurements to ensure a proper fit and avoid damaging the glass or frame during installation. Allowing wiggle room ensures a safe, secure, and long-lasting installation.

Tolerance for Manufacture

In the manufacture of double and triple glazed units, a tolerance of +2mm and -1mm is established to accommodate the slight variations that can occur during the production process. This means that the dimensions of each unit can be positively adjusted by up to 2mm, allowing for minor oversizing, or negatively adjusted by 1mm, which accounts for minor undersizing. Such tolerances are crucial to ensure a proper fit within the window frame, aiding in the installation process and promoting optimal thermal efficiency. By allowing for these variances, manufacturers can help avoid potential fitting issues that might arise from changes in temperature, humidity, and material expansion or contraction over time. This careful attention to manufacturing tolerances ultimately contributes to the durability and performance of the triple or double glazed units over their lifespan.

Rebate Width

Generally, around 10mm to 15mm, this width ensures the unit is securely held in place, allowing sufficient room for the glass and any beading used to hold the unit.

Reflective Glass

A type of glass coated with a metallic or ceramic layer to reduce heat gain and glare. Commonly used in office buildings and solar control applications, reflective glass helps regulate indoor temperatures and improve energy efficiency.

Reinforced Glass

Glass that has been strengthened using materials such as wire mesh, coatings, or laminates. It enhances impact resistance and security and is often used in high-risk environments like prisons, banks, and industrial settings.

R-value (Thermal Resistance)

A measure of a material’s resistance to heat flow. Higher R-values indicate better insulation, making triple-glazed or gas-filled units more effective at maintaining indoor temperatures.

Safety Glass

A type of glass designed to minimise the risk of injury when broken. It is stronger than regular glass and used in applications requiring extra protection. The two main types are tempered glass, which shatters into small, rounded pieces, and laminated glass, which holds together when broken due to a plastic interlayer. Commonly used in vehicle windscreens, windows, glass doors, and protective barriers.

Sandblasted Glass

A type of obscure glass created by blasting the surface of the glass with fine sand particles at high pressure. This process results in a frosted or matte finish, which obscures visibility while still allowing light to pass through. Sandblasted glass is often used for privacy in spaces like bathrooms, shower doors, office partitions, and decorative features. It can also be used for creating custom designs or patterns on the glass surface.

Sealant

A material used to fill gaps, joints, or seams in construction or manufacturing to prevent the passage of air, water, or other substances. In glazing, sealants are typically applied around the edges of glass panels to secure them within the frame and provide a weatherproof seal. Sealants help improve energy efficiency by preventing drafts and moisture ingress.

Sealant Types for Glazing

Butyl Glazing Compound: A traditional, non-hardening putty used for sealing glass in frames. It provides effective sealing properties, preventing drafts and water infiltration. However, because it doesn’t harden, it remains flexible and can be applied for a variety of glazing applications.

Silicone Sealants (Silfix U9): Known as one of the best options for bedding in double-glazed units. Silfix U9 is a high-quality, durable sealant that ensures a strong, waterproof bond between the glass and the frame. It is resistant to weathering and UV degradation, making it ideal for outdoor applications.

Low Modulus Neutral Cure (LMN) Silicone: A clear silicone used to fill the remaining void around the glazing unit and secure wooden beads in place. LMN silicone is non-corrosive and cures without producing harmful by-products, making it safe for use with double-glazed units. Avoid using standard acetoxy-cure silicone, as it can release acidic compounds that may damage the seal of double-glazed units, compromising their integrity.

Each of these sealants serves a different purpose in the glazing process, providing flexibility, durability, and strong sealing to ensure the longevity and performance of double-glazed windows.

Sealed Glass Unit (SGU)

A double-glazed, triple-glazed, or single-glazed unit where the glass panes are sealed together with a spacer bar and filled with insulating gas (e.g., argon or krypton) to improve thermal efficiency.

Secondary Double-Glazed Unit

A glazing system where a secondary pane of glass is added to an existing single-glazed window, creating an air gap between the two layers. This setup provides additional insulation, improving energy efficiency and reducing noise while still maintaining the original frame. It's often used in retrofit applications where replacing the entire window is not possible or desired.

Self-Cleaning Glass

Self-cleaning glass features a special hydrophilic and photocatalytic coating that breaks down organic dirt and allows rainwater to wash it away, reducing the need for manual cleaning. It uses a transparent coating that reacts with sunlight to break down dirt, ensuring a cleaner and clearer glass surface with minimal maintenance. Read more...

Silicone Sealant

A flexible and weather-resistant sealant used to bond and seal glass edges in sealed units. It prevents moisture ingress and enhances durability, especially in external glazing applications.

Single Glazing also known as Single Pane

A type of window where only a single pane of glass is used, without any additional layers or insulation. It offers basic protection against the elements but has lower thermal efficiency and sound insulation compared to double or triple glazing. Single glazing is typically found in older buildings.

SKN176 Cool-Lite

This is a solar control coating to help regulate indoor temperatures by reflecting excess solar heat while maintaining natural light. A high-performance solar control glass with Low-E properties, offering a balanced combination of natural light transmission and solar heat reflection. It is ideal for large, glazed areas, reducing overheating while maintaining a comfortable indoor environment.

Softcoat

A type of Low Emissivity (Low-E) Glass that features a clear coating applied to the inside of the inner pane. This coating reflects heat back into the building, improving thermal insulation and helping to maintain a comfortable indoor temperature by reducing heat loss. Softcoat glass is commonly used in windows and glazing to enhance energy efficiency.

Solar Control Glass

A glass type designed to reduce heat transfer by reflecting or absorbing solar radiation. It helps maintain cooler indoor temperatures and reduces the reliance on air conditioning in hot climates.

Spacer Bar

A component used in double-glazed units to maintain the gap between the two panes of glass. This gap is typically filled with argon or krypton gas, which are inert gases known for their thermal insulation properties. The spacer bar is typically made of materials like aluminium or composite materials and ensures the proper separation of the glass panes. The gas within the gap helps reduce heat transfer, improving the energy efficiency of the window. The spacer bar is usually covered by the window frame or beading after installation to provide a clean, finished look.

Spacer Bar Sightline

The height of the spacer bar that is typically hidden once the window unit is installed, covered by the retaining bead and frame. The sightline refers to the portion of the spacer bar visible before installation, and it is important for determining the alignment and aesthetic appearance of the window or glazing unit.

Stained Glass

Glass that has been coloured, painted, or textured for artistic and decorative purposes. It is commonly seen in churches, historic buildings, and luxury interiors.

Tempered Glass

Tempered glass is glass that has been heat-treated to increase its strength and resistance to thermal stress, making it safer and less likely to shatter upon impact.

Thermal Expansion

The property of glass that causes it to expand or contract with temperature changes. Understanding this is crucial in designing glazed units to prevent stress fractures and seal failures.

Tinted Glass

Glass that has been infused with colour during manufacturing to reduce glare and heat transmission. Common colours include grey, bronze, blue, and green, each with different levels of solar control.

Toughened Glass (Tempered Glass)

Glass that has undergone a heating and rapid cooling process to increase its strength. When broken, it shatters into small, blunt pieces rather than sharp shards, making it ideal for doors, shower enclosures, and vehicle windows.

Toughened Laminated Glass

A combination of toughened glass and laminated glass, offering both impact resistance and shatterproof properties. It is widely used in high-security glazing and roof installations.

Triple Glazed

A type of window featuring three panes of glass with two insulating air or gas-filled gaps between them. This provides enhanced thermal insulation, better soundproofing, and increased energy efficiency compared to double glazing. Triple glazing is ideal for colder climates and buildings seeking superior comfort and heat retention.

Ultraviolet Light (UV)

Invisible radiation with wavelengths shorter than visible light. UV can cause skin damage and material degradation. UV-blocking coatings in windows help protect against fading and damage.

UV Protection Glass

Glass that reduces ultraviolet radiation penetration, preventing fading of furniture, flooring, and artwork. Laminated glass and Low-E coatings often include UV protection properties.

U-Value

In double-glazed units, the U-value measures the rate of heat transfer across the entire glazing system, which consists of two panes of glass with an air or gas-filled space between them. The lower the U-value, the better the unit is at insulating and preventing heat loss.

Double glazing improves insulation compared to single glazing by creating an air or gas barrier (such as argon) between the panes, which reduces the amount of heat that can pass through. The U-value of a double-glazed unit considers factors like the type of glass used, the thickness of the air gap, and the quality of the seal.

Generally, modern double-glazed units have U-values ranging from 1.0 to 1.5 W/m²K, with lower values indicating better insulation. The U-value is an important factor in determining the energy efficiency of windows and is often used to assess the effectiveness of the glazing in reducing heating costs.

Warm Edge Spacer Bars

Made from plastic or other materials, these spacer bars improve the thermal performance of double-glazed units by reducing heat loss. Unlike aluminium, which conducts heat, warm edge spacer bars help minimize thermal bridging, enhancing energy efficiency and reducing condensation on glass.

Wet Fitting

This method involves using sealant (such as silicone or another adhesive) to secure a glazing unit in place. Unlike dry fitting, where the unit is held by pressure alone (e.g., with beading or gaskets), wet fitting adds an extra layer of security and helps create a better seal between the unit and the frame, improving insulation and preventing leaks.

Wire Glass

Glass embedded with a wire mesh, providing fire resistance and impact protection. It is commonly used in industrial applications and fire-rated doors.