TECHNICAL TERMS | S-COOL Window Films

Absorption

The portion of solar energy that is absorbed by the glazing expressed as a percentage.

Acid Etched / Privacy Film

An effect obtained by specialist window film similar to acid etched glass that diffuses light but keeps the visible light transmission to high levels.

Annealed Glass

Glass is made by a process of heating and mixing its constituents; annealed glass is produced from the hot liquid as a thin sheet, which is allowed to cool and harden under controlled conditions.

B Value

A measure of the amount of solar energy that enters the building by reflection and by absorption/re-radiation compared to the performance of 3 mm clear glass; it was used particularly in Germany but has been superseded by the European standard g value.

Blackout Film

Film, black in colour, that has visible light transmission close to 0 % (typically < 0,25 %).

Break Strength

The ability of window film of a given type and thickness to resist breaking. The measurement is given in terms of force per unit width, such as Newtons per 25 mm or pounds per inch. Break strength varies greatly with film thickness and substrate type and is used to demonstrate the absolute strength of a strip of the material of a given width.

BTU Meter

A device that measures solar energy intensity and gives solar intensity in either W/m² or BTU/ft².hour. It is used to compare the solar intensity entering through glazing with and without solar control window film.

BTU-British Thermal Unit

The amount of heat energy required to raise the temperature of one pound of water one degree Fahrenheit. 1 BTU = 252 Calories (Cal). The BTU has been superseded by the metric Joule; 1 BTU = 1054,35 Joules.

Cure Time

The time required for the water used in the installation solution to evaporate from between the film and the glass and for the film's adhesive system to reach maximum bond strength.

DGU

Double Glazed Unit, also known as double glazing. Modern forms contain coatings and/or gas fillings to improve their insulating properties and are known as IGUs or Insulating Glass Units.

Direct Solar Reflection

The portion of solar energy that is reflected by the glazing expressed as a percentage. Not to be confused with Total Solar Energy Rejection.

Direct Solar Transmission

The portion of solar energy that passes directly through the glazing into the building expressed as a percentage.

Dry Adhesive

An adhesive that is initially dry to the touch but is activated by water; pressure sensitive adhesives are sticky to the touch. It provides a very hard and extremely durable chemical bond to the glass with no optical distortion which can sometimes occur with thicker PS adhesives. Used in window film for architectural applications for maximum durability and optical clarity. Cure time can vary according to film type, temperature, and humidity but in reasonable environmental conditions is normally about 7 days.

Dual Reflectance

A window film that has higher visible light reflectance to the outside than to the inside in order to improve ease of viewing to the outside, especially at night.

Dyed Film

A window film with a colour added within its structure.

E-Beam Deposition

A manufacturing process used to deposit layers of metal or alloys (even those with high melting points) onto polyester film surfaces using an electron beam; very fast deposition rates are possible.

Edge Retention System

A system that provides a means of additionally securing a safety film + glass combination to the frame, for example by adhering to both the film and the frame.

Electromagnetic Radiation

Electromagnetic radiation concerned with glazing includes UV light, visible light, infra red heat; solar radiation contains all these components. Solar radiation concerned with glazing is not radioactive.

Electromagnetic Spectrum

The electromagnetic spectrum includes infra-red energy, visible light and UV light. It includes wavelengths from more than 100 000 kilometres (with a frequency of 3 Hertz) to wavelengths of 0,000000001 millimetres (with frequencies of > 1020 Hertz). The solar radiation that reaches Earth is a very small part of this range, typically 300-2500 nm (0,0000003 to 0,0000025 metres).

Elongation at Break

The percent increase in length of a sample of film at break when tested according to a recognised test method. Elongation is the film's ability to stretch without breaking.

Emissivity

A measure of the ability of a surface to absorb and re-radiate energy; in simple terms, emissivity is the fraction of long wave infra-red energy remaining after reflection back to the source. A low value reduces the rate of heat flow through the glazing; window film can reduce emissivity of glazing to less than 0,4. Example: An emissivity of 0,33 means that 67 % of the long wave infra-red energy is reflected back to the source.

Energy Savings

The savings that can be achieved in air conditioning costs by using solar control window film to reduce the amount of solar energy entering into a building through the glazing. Often these savings are incorporated into whole building energy savings. Some low Emissivity film will provide air conditioning savings in the summer and heating savings in the winter, thereby increasing annual savings beyond that of traditional solar control film.

Fading and Fade Reduction

Fading is seen as colour changes in fabrics, paintings, furniture, etc. and is caused by Ultra Violet light, visible light, infra red energy, air humidity and other factors. Fading cannot be stopped but the rate of fading can be reduced. Window film can help to reduce fading, for example by reducing UV transmission to < 0,1%. Materials that fade quickly in sunlight cannot normally be protected sufficiently by window film against fading.

Far Infra-Red

Wavelengths of electromagnetic radiation range from 780nm to about 60 000 nm. Near infra-red is about 780-2500 nm, while far infrared is about 2500-60 000 nm. Solar radiation contains a large amount of near infra-red radiation between 780 nm to 2500 nm; room energy (room heat) is normally felt in the far infra-red region. Infra-red radiation is not radioactive.

Film Thickness

Thickness of window film is usually measured in microns (millionths of a metre or thousandths of a millimetre).

Film to Glass Thermal Stress Compatibility

There is a wide range of window film that is suitable for installation to existing and new glazing. However, in some situations an incorrectly specified window film can cause thermal stress breakage of float glass. Window film manufacturers provide good guidelines on the thermal stress compatibility of each of their films with different glazing systems. Note that glass always has a risk of thermal stress breakage whether window film is installed or not; this risk is insignificant for tempered glass, negligible for heat strengthened glass, and low for float glass. The installation of correctly specified window film will maintain the risk of thermal stress breakage to low levels, provided that the glass is undamaged and meets accepted standards.

Fire Safety

Window film, if correctly installed, when burnt has low risk of propagating and spreading a fire, low toxicity, and low smoke emission.

Float Glass

Float glass made by the process developed by Pilkington using hot liquid tin – the hot liquid glass floats on the liquid tin surface. The hot glass is slowly cooled to release internal stresses from the glass and thereby enable the glass to be used in other processes such as cutting to specified sizes. Over 90 % of annealed glass worldwide is made by the float method.

Glare Reduction

The percentage reduction in the amount of visible light transmitted by the glazing compared with that transmitted by 3 mm clear glass; window film can provide Glare Reduction of up to 95 %.

Glass Strength

Glass does not have one specific strength but a range of strengths. Glass strength is dependent upon a number of factors including thickness, type, processing conditions, and whether it is damaged or not. Type of glass: As a guide, heat strengthened glass is up to 3 times stronger than float glass and tempered glass is up to 5 times stronger than float glass.

Glass Surface

Glazing surfaces are counted starting at the exterior surface and finishing at the interior surface; a double glazed unit of two panes of glass separated by an air space has four glass surfaces.

Global Warming

The effect identified by scientists of world temperatures increasing because of carbon dioxide emissions from the burning of coal, oil, gas and other fuels. Sometimes called the Greenhouse Effect of the Earth.

Graffiti

Unwanted damage to glass and other surfaces by scratching, painting, etching and other means; window film can protect glass and other surfaces against graffiti.

Greenhouse Effect

The effect where interior of buildings, vehicles, etc. increase in temperature by the transmission of solar radiation through the glazing but, because glazing is more opaque to long wave than short wave infra-red energy, this heat cannot escape easily and the interior compartment increases in temperature, often to uncomfortable levels.

Hazard Rating

A system of rating the hazard produced from glass shattered in an explosion. Hazard ratings are obtained from standardised tests and range from No Hazard to High Hazard.

Heat Loss Reduction

An amount of energy is transferred through glazing by conduction, convection, and radiation; the higher the rate of energy transfer, the greater the heat loss in winter. The addition of an insulating window film to a glazing system reduces the loss of energy, i.e. reduces heat loss usually from the building to the outside, and is expressed as a percentage.

Heat Mirror

A window film that has high visible light transmission relative to its solar energy rejection. These films are solar control products and are also termed spectrally selective products because they select for high visible light transmission and reduced solar energy transmission.

Heat Strengthened Glass

A glass that has been through an additional heat treatment process to make it 2-3 times stronger than annealed glass.

IGU

Glazing constructed from two panes of glass; the main use of insulating glass is to reduce the rate of heat flow through the glazing. Insulating Glass Units are often used to reduce heat loss from buildings in the winter, but are also used in hot climates to reduce solar heat gain by the building. Modern Insulating Glass Units have coatings on one or both surfaces that face in towards the space between the two panes of glass; these coatings reduce energy transfer through the glazing and are nowadays significant in reducing energy consumption.

Infra-Red Radiation

Wavelengths of electromagnetic radiation from 780 nm to about 60 000 nm; near infra-red is about 780-2500 nm and far infra-red is about 2500-60 000 nm. Solar radiation contains a large amount of infra red radiation between 780 nm to 2500 nm. This type of radiation is not radioactive.

Installation Solution

Solution used during the installation of window film; it is specifically used to assist with film positioning and to prevent too-fast adhesion of the film to the glass.

K Value

K value is an obsolete term and has been replaced by the U value.

Laminated Film

Window film made from two or more layers of polyester or other film adhered together with an adhesive.

Laminated Glass

Laminated glass is made from two or more pieces of glass with a plastic interlayer, usually polyvinylbutyral (PVB). Annealed, heat strengthened or tempered glass can be used to produce laminated glass. Laminated glass, if constructed correctly, is a safety glass and is designed to either not break or to break safely upon impact with a low risk of injury from broken glass fragments.

Low-E or Insulation Film

Window film with low emissivity coating(s) designed to reduce heat loss through glazing.

Luminous Efficacy

A measure of how effective a glazing product is in rejecting solar energy but retaining good visible light transmission. A number greater than 1,0 indicates that the film or glazing unit is "spectrally selective," blocking more of the near infra-red than the visible light components of the solar spectrum. It is calculated according to the equation LSG = visible light transmittance / g value.

Metallising

A manufacturing process used to deposit a metal onto polyester film surfaces by evaporation; the metal is usually Aluminium. Metallised window film provides excellent solar control.

Micron

One millionth of a metre or one thousandth of a millimetre.

Nanometre or nm

One millionth of a millimetre or 0,000000001 m.

Near Infra-Red

Wavelengths of electromagnetic radiation range from 780 nm to about 2500 nm. Near infra-red is about 780-2500 nm while far infrared is about 2500-60 000 nm. Solar radiation contains a large amount of near infra-red radiation between 780 nm to 2500 nm; room energy (room heat) is normally felt in the far infra-red region. Infra-red radiation is not radioactive.

Optical Properties

Solar-Optical properties of glazing – including window film on glass – are determined in accordance with EN 410 “Glass in building. Determination of luminous and solar characteristics of glazing”. According to EN 410, the most important values are the visible light transmission and the g value. Other properties such as solar energy transmission, visible light reflection, etc. can also be obtained using EN 410.

Peel Strength

The adhesive strength of a window film in grams per 25 mm width, and is usually tested in accordance with an appropriate standard. It is generally measured as the force required to peel the film from the glass using a peel angle between the film and the glass of close to 180°. Safety and security film has high peel strength.

Performance Time

The time required for safety / security film to achieve a minimum level of safety performance to an impact test such as EN 12600. This can be as low as a few hours but very thick and/or metallised and/or sputtered versions can take 1-3 days. Installation quality has a very significant effect on the time needed to achieve a minimum level of performance.

Polyester Film

Polyester, as a biaxially oriented film, is the main constituent of window film; it has excellent optical clarity and strength. Its chemical name is polyethylene terephthalate, abbreviated to PET.

Polyvinyl Butyral

PVB, or Polyvinyl Butyral, is a material used to adhere glass layers together to make traditional laminated glass. Window safety film can be adhered to the surface of existing glazing to modify the glazing to a safety material with breakage like laminated glass.

Pressure Sensitive Adhesive (PSA)

Pressure sensitive adhesive is sticky to the touch and remains so during its lifetime. It provides faster adhesion to glass than dry adhesives but durability can be lower; a small amount of optical distortion may be present, especially for safety and security film. DPS (Detackified Pressure Sensitive) adhesives are simply PS adhesives coated with a water soluble layer (intended to prevent the film from sticking to itself as the liner is removed) which must be washed away before the film installation. Cure for PS film averages three days, though this time is a function of temperature, humidity, and film type and may require up to 30 days in some situations. Some safety and security film can take longer to achieve full cure but this should not be confused with time to achieve performance.

Privacy Film

Window film that, once correctly installed, reduces or prevents vision through glazing.

Puncture Strength

The puncture strength of a window film is given in kilograms or pounds. It is generally measured using a standardised test method as the resistance the film gives to a blunt probe forced through it.

PVB

PVB, or Polyvinyl Butyral, is a material used to adhere glass layers together to make laminated glass.

Release Liner

A disposable plastic film covering and protecting the adhesive layer on the window film.

Safety and Security Film

Window film that, when correctly installed to glass, modifies the glass to one or more of the following:

a safety glazing impact resistant material according to a recognised standard such as EN 12600 “Glass in building. Pendulum test. Impact test method and classification for flat glass”;
a security glazing material resistant to manual attack according to a recognised standard such as EN 356 “Glass in building. Security glazing. Testing and classification of resistance against manual attack”;
a security glazing material resistant to bullet attack according to a recognised standard such as EN 1063 “Glass in building – Testing and classification of resistance against bullet attack”;
a security glazing material resistant to explosive pressures according to a recognised standard such as EN 13541 “Glass in building – Testing and classification of resistance against explosion pressure”

Window film has been extensively used for protection against deliberate attack on glazing, and is regularly specified by Governments and commercial organisations for protection against glass shattered in an explosion.

Safety Glazing

Glazing which complies with the requirements of an impact test; EN 12600 is the European standard for assessing safety glazing. Window film is normally used to modify float glass to safety glazing materials; window film has been extensively tested to prove compliance with EN 12600 on a variety of float glass thicknesses.

Scratch or Abrasion Resistant Coating

A coating on the surface of many window films, applied during the manufacturing process, that resists abrasion; it is usually hard.

Security Glazing

There are various types of security glazing and specification needs to be careful to ensure the correct type is selected. Security glazing can resist manual attack (EN 356), reduce the effects of an explosion, or reduce the effects of bullet attack.

Shading Coefficient

A measure of the amount of solar energy that goes to the inside of the building by reflection and by absorption/re-radiation compared to the performance of 3 mm clear glass; it is being superseded by the g value.

Solar Control

Reduction by the glazing of the amount of solar energy passing through the glazing.

Solar Control Window Film

Window film that, once correctly installed, provides Solar Heat Gain Reduction, Glare Reduction, Fading and Fade Reduction, or a combination of these properties. Benefits include reduced summer temperatures inside buildings, reduced air conditioning costs, reduced eye strain, and reduced fading and damage to paintings, furniture, carpets, etc.

Solar Energy

The energy from the sun reaching the Earth’s surface; it is generally in the wavelength range of 300-2500 nm. This type of radiation is not radioactive.

Solar Energy Absorption

The portion of solar energy that is absorbed by the glazing expressed as a percentage.

Solar Energy Damage

UV is not the only cause of fading and damage to property; visible light and infra-red energy also cause damage.

Solar Energy Reflection

The portion of solar energy that is reflected by the glazing expressed as a percentage. Not to be confused with Total Solar Energy Rejection.

Solar Energy Rejection

The total amount of solar energy that goes to the outside of the building by reflection and by absorption/re-radiation.

Solar Energy Transmission

The portion of solar energy that passes directly through the glazing into the building expressed as a percentage.

Solar Energy Transmittance

The portion of solar energy that passes directly through the glazing into the building expressed as a decimal.

Solar Factor

The total amount of solar energy that enters the building by reflection and by absorption / re-radiation; it is the same as the g value but is often given as a percentage, meaning Solar Factor % = g x 100. Window film can modify glazing to give g values less than 0,20 and in some cases less than 0,10. See also EN standards.

Solar Heat Gain

The solar energy gained by a building from the sun and experienced as heat and / or as a temperature increase. Solar control window film can give significant reduction in solar heat gain.

Solar Heat Gain Coefficient

The total amount of solar energy that enters the building by reflection and by absorption / re-radiation; it normally refers to American methods of calculating a value similar to the European g value. Window film can modify glazing to give g values less than 0,20 and in some cases less than 0,10. See also EN standards.

Solar Heat Gain Reduction

The reduction in solar energy gained by a building from the sun, often by the addition of Solar Control Window Film.

Solar Overheating

This occurs when solar energy entering the building causes room temperatures to be too high for workplace comfort. Solar control window film can considerably reduce solar overheating.

Solar-Optical Properties of Glazing

Spectrally Selective

Glazing that allows high visible light transmission with good solar energy rejection. See Luminous Efficiency.

Sputtering

A manufacturing process used to deposit layers of metal, alloys, oxides, etc. onto polyester film surfaces; the process itself does not make the product better than metallised film, but the metals, alloys, etc. offer alternative properties to Aluminium.

Strength of Glass

Tempered Glass

Glass, treated by heating and rapid cooling, to make it 3-5 times stronger than annealed glass.

Tensile Strength

The maximum force per original cross section area that a material resists before breakage when tested according to a recognised test method. The Tensile Strength of a material should not vary with thickness (for the same material of the same composition, tested in the same direction and under the same conditions), but does for polyester film of different thickness because of some variation in the crystallinity of polyester film with thickness.

Thermal Comfort

The condition, including reasonable temperature and glare levels, that allows building occupants to be comfortable with the environmental conditions. Solar control and insulation window film can give significant improvements in thermal comfort.

Thermal Stress

Stress in a glass pane caused by one part of the glass pane being at a different temperature from another part of the same glass pane.

Thermal Stress Breakage

A break in glass that is caused by thermal stress; the typical feature of a thermal stress breakage in glass is that the break commences at 90° to the edge of the glass. All glass has a risk of breakage due to thermal stress regardless of whether window film is applied or not; this risk is insignificant for tempered glass, negligible for heat strengthened glass, and low for float glass. See Thermal Stress Compatibility.

Thermal Stress Compatibility

There is a wide range of window film that are suitable for installation to existing and new glazing. However, in some situations an incorrectly specified window film can cause thermal stress breakage of float glass. Window film manufacturers provide good guidelines on the thermal stress compatibility of each of their films with different glazing systems. Note that glass always has a risk of thermal stress breakage whether window film is installed or not; this risk is insignificant for tempered glass, negligible for heat strengthened glass, and low for float glass. The installation of correctly specified window film will maintain the risk of thermal stress breakage to low levels, provided that the glass is undamaged and meets accepted standards.

Thermal Stress Strength of Glass

In normal architectural and automotive uses: tempered glass will not break from thermal stress, heat strengthened glass is very unlikely to break from thermal stress, but float glass is susceptible to breakage from thermal stress. When adding a window film to existing glazing, the supplier should always check the glazing for thermal stress compatibility between the window film and the glazing.

Tinted Film

A window film with a colour added within its structure.

Total Solar Absorption

The portion of solar energy that is absorbed by the glazing expressed as a percentage.

Total Solar Energy Rejection

The total amount of solar energy that goes to the outside of the building by reflection and by absorption/re-radiation.

Total Solar Reflection

The portion of solar energy that is reflected by the glazing expressed as a percentage. Not to be confused with Total Solar Energy Rejection.

Total Solar Transmission

The portion of solar energy that passes directly through the glazing into the building expressed as a percentage.

Toughened Glass

Glass, treated by heating and rapid cooling, to make it 3-5 times stronger than annealed glass.

Transverse Direction (TD)

The direction across the width of a roll of window film.

U Value

The U value is a measure of the rate of heat transfer through the glazing (or other building material) and is given in units of W/m².K. A method of calculating the U value of glazing is given in EN 673 “Glass in building. Determination of thermal transmittance (U value). Calculation method”.

UV Transmission

The portion of Ultra Violet light that passes directly through the glazing into the building expressed as a percentage.

UV Transmittance

The portion of Ultra Violet light that passes directly through the glazing into the building expressed as a decimal.

Vapour Deposition

There are several different definitions of vapour deposition. For example, metallising can be regarded as a form of physical vapour deposition where Aluminium metal is evaporated as a vapour onto polyester film; sputtering uses an ionised plasma that some people regard as a vapour. Chemical vapour deposition (CVD) deposits atoms (or molecules) from a chemical vapour.

Visible Light Reflectance

The portion of visible light that is reflected by the glazing expressed as a decimal. Usually the visible light reflectance is given for both exterior and interior sides of the glazing.

Visible Light Reflection

The portion of visible light that is reflected by the glazing expressed as a percentage. Usually the visible light reflection is given for both exterior and interior sides of the glazing.

Visible Light Transmission

The portion of visible light that passes directly through the glazing into the building expressed as a percentage.

Visible Light Transmittance

The portion of visible light that passes directly through the glazing into the building expressed as a decimal.

Window Film

Window film is a self-adhesive film that is applied to glass and glazing systems to modify the properties of the glass / glazing. The properties that can be modified include solar control, safety, security, privacy, insulation, UV filtering and fade reduction, and decorative.