The world of window film and architectural finishes is nuanced and complex. You may find these definitions useful as you navigate the industry.
Ambient is the surrounding or encompassing atmosphere.
Manufactured by pouring molten glass onto a bed of molten tin which is then cooled, annealed glass is the product that most people think of as "plate" glass. This flat glass product has little residual surface compression and must be handled with care to minimize thermal stress. Unlike tempered glass, annealed glass breaks into sharp shards when shattered. 3M Safety & Security Window Film can make annealed glass tempered by most local building codes.
Art / Opalescent / Cathedral Glass
Colored translucent glass, often called art glass, opalescent glass, cathedral glass or stained glass, is also produced by the rolling process, but generally in small, batch type operations. There are usually variegated colors within each sheet produced and no two sheets will match for hue. Thickness will vary within a sheet as well as from sheet to sheet. The maximum thickness produced is usually 1/8". When used as a glazing material, art glass should be glazed in the same manner as tinted / heat absorbing glass. Art glass cannot be tempered.
An attachment system is a chemical or mechanical restraint system that improves the performance of security window film during blasts, high winds, and smash-and-grab break-ins. 3M’s proprietary chemical attachment system is called 3M Impact Protection Adhesive.
A blast is a temporary change in the gas density, pressure and velocity of the air surrounding an explosion point. If the initial change is discontinuous, it is referred to as a shock wave. If the initial change is gradual, it is known as a pressure wave. 3M’s Safety & Security Window Films are designed to mitigate the effects of a bomb blast by holding together in place nearby glass, thereby helping to protect people, property, and continuity of operations.
Blast Over-Pressure is the violent rise in air pressure above normal atmospheric pressure (14.786 pounds per square inch). It is a term that is used when bomb blast testing fragment retention film.
BTU (British Thermal Units)
British Thermal Units (abbreviated BTU) are the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit (1 BTU = 252 Calories). It is a term that is used to quantify the benefits of sun control window films such as 3M Prestige Series and insulating window films such as 3M Thinsulate Series.
Clear Glass consists of silica sand with added alkaline salts such as lime potash and soda. It is colorless and has a visible light transmittance ranging from 75% to 92%, depending upon thickness. It constitutes the bulk of the flat glass that is used.
Daylight Application (Installation)
A daylight application is the process of applying window film to a piece of glass from edge to edge. A small untreated area of glass remains, which is referred to as a “daylight gap”. An alternative method for installing safety and security window film is to use an attachment system.
Drag is the negative pressure effect felt on the rear face of a structure as the blast wave moves away from the building. It is a term that is used when bomb blast testing fragment retention film.
Emissivity is the ratio of radiant energy emitted by a surface to the radiant energy emitted by a black body of the same temperature. It is a term that is used for insulating window films such as 3M Thinsulate Climate Control Series.
An explosion is the sudden release of energy resulting in a blast wave. It is a term that is used when bomb blast testing fragment retention film.
Figured / Patterned Glass
Figured / Patterned Glass is produced domestically by the continuous pour process in thicknesses of 1/8" to 7/32". A pattern etched on one or both rollers is reproduced on the glass. Colors are available but are extremely limited. This type of glass is frequently called "obscure" or "decorative" glass. The pattern diffuses detail of objects viewed through the glass; it does not obscure them. The degree of diffusion achieved is a function of the pattern and whether the pattern is on one or both sides. Some patterns cannot be tempered for safety glazing use because of their depth. Patterned glass can be simulated by installing 3M Glass Finishes on clear glass.
The float glass process accounts for over 90% of the flat glass presently produced in the United States. In this process, molten glass is poured continuously from a furnace onto a large bed of molten tin. The molten glass literally floats on the tin, spreading and seeking a controlled level in the same manner as water poured onto a smooth, flat surface. In the controlled level seeking process, the molten glass is allowed to spread to width of 90" to 140", depending upon the furnace size and glass thickness being produced. The glass slowly solidifies as it travels over the molten tin. It is then cooled under controlled conditions. Afterward, it emerges as a continuous ribbon of glass at essentially room temperature. The product is now flat, fire-finished, and with virtually parallel surfaces.
Glass Edge Strength
Glass is made to withstand from between 3,000 to 5,000 psi (210 to 350 kg/cm) of edge stress. When edge stress exceeds edge strength, breakage occurs. Edge strength depends on glass size, thickness, how it is cut, and treatment of edge by glazier. A straight clean edge is the strongest. Damaged edges can reduce edge strength by up to 50%. Because glass can break due to thermal stress (edge stress > edge strength), it is important to contact a 3M Dealer when choosing a window film solution.
Ground Zero is the location at which an explosion occurs. It is a term that is used when bomb blast testing fragment retention film.
Heat Strengthened Glass
Heat Strengthened Glass is fabricated by a process like that of tempered glass. Some equipment can produce both. The glass is heated to approximately 1,100° F and the cooling process is slower than for tempered glass. The strength developed is about twice that of annealed glass.
Hot Spots are the areas particularly affected by solar radiation and the imbalance of solar energy. 3M Sun Control and Insulating Window Films are designed to reduce, if not eliminate, hot spots.
Impulse is the amount of energy generated in an explosion. It can be either positive (impact force) or negative (suction force) energy. Impulse is measured by integration of the pressure / time curve recorded in an explosion. It is a term that is used when bomb blast testing fragment retention film.
Insulated Glass units consist of two panes of glass that enclose a hermetically sealed air space. The panes are held apart by a spacer around the entire perimeter. The spacer contains a moisture absorbent material called a desiccant that serves to keep the enclosed air free of visible moisture. Double pane glass has a lower U-Value than single pane and a higher U-Value than triple pane. 3M Thinsulate Climate Control Window Film is designed to turn single pane glass into double pane, and double pane glass into triple pane, all at a fraction of the price of window replacement.
Laminated Glass consists of two or more plies of glass interleaved with clear or tinted polyvinyl butyl (PF). The application of heat and pressure bonds the glass and plastic interlayer into one unit. When laminated glass is fractured, the particles of glass tend to adhere to the plastic, affording protection against flying or falling particles. Some combinations of glass and plastic thicknesses do qualify as safety glazing materials under the criteria of ANSI Z97.1 and CPSC 16 CFR 1201. Installing 3M’s Safety & Security Window Films to non-laminated glass can often duplicate the performance of laminated glass.
A lite is a sheet or pane of glass. Any 3M window film product is applied to the glass pane, usually in a retrofit application.
Low-emissivity coatings (Low-E) reflect that part of the heat spectrum above 3,000 millimicrons wavelength that is called "sensible heat". The heat from hot water or steam radiators and the heat from hot air ducts from a furnace are typical examples of this kind of heat. These coatings have high visible light transmission. In fact, they are nearly invisible on the glass. The visible light transmission is typically about 20 percentage points below that of an equivalent uncoated glass. The major attribute of Low-E insulating units is their sensible heat reflecting character which is apparent from their low U-values. Low-E coatings are applied to glass by vacuum processes and by pyrolytic processes. Installing an insulating film like 3M Thinsulate Climate Control Window Film adds a Low-E reflective coating to standard glass and is like turning single pane glass into double pane, and double pane glass into triple pane, all at a fraction of the price of Low-E window replacement.
Luminescent Coefficient is the rate of visible light transmission and shading coefficient (Ke ratio). This is a relationship between how much heat gain is rejected and the amount of visible light transmitted.
Most mirrors are manufactured by the wet chemical deposition method, although a few, for specialized use, are made by vacuum deposition. Safety mirrors are available to meet various laws and building codes. A mirror made from tempered glass will have the inherent distortion from the tempering process and cannot have the same quality in reflection as laminated ones made from mirror quality annealed float glass. One-way mirrors, which are often called two-way mirrors, are designed to allow vision through from one direction while presenting a mirror appearance from the opposite side. Their major application is to permit undetected observation for study or surveillance in places such as prisons, gambling casinos and psychiatric treatment centers. A difference in lighting level is necessary; in the room to be studied the lighting level should be at least five times greater than the lighting level in the observation room; ten times greater is even more effective. Two-way mirrors are not intended for use in exterior walls. 3M’s one-way mirror film can turn clear glass into a one-way mirror.
The negative phase is the portion of a blast wave, also known as the "suction phase", whose pressure is below ambient. It is a term that is used when bomb blast testing fragment retention film.
A pane is a glass-filled division of a window, door, or wall, or the glass by itself. Any 3M window film product is applied to the glass pane, usually in a retrofit application.
Plate Glass, manufactured by the grinding and polishing process, is no longer produced in the United States, and words referring to it have been eliminated from the ASTM Specification C103685. It has been replaced by the float glass process.
The positive phase is the portion of a blast wave whose pressure is above ambient. It is a term that is used when bomb blast testing fragment retention film.
Reflected Pressure is the amount of pressure felt by an object standing directly in the path of an expanding blast wave. It is a term that is used when bomb blast testing fragment retention film.
Reflective Glass is a clear or tinted glass coated with an extremely thin layer of metal or metallic oxide. Reflective glass can be simulated using any number of 3M window film products.
The rolled glass process consists of pouring molten glass from a furnace, then feeding it through rollers to produce the desired thickness. The glass ribbon is then cooled under controlled conditions. There are three general types of rolled glass: figured / patterned, wired and art / opalescent / cathedral glass.
Shading Coefficient is the ratio of solar heat gain passing through a glazing system to the solar heat gain that occurs under the same conditions if the window were made of clear, unshaded, double strength window glass. The lower the number, the better the shading qualities of the glazing system. Often abbreviated as Shading Coefficient (SC), it is a term that is used to evaluate the performance of a sun control window film such as 3M’s Prestige Series.
The sheet glass process accounts for a very small portion of U.S. glass production. Some imported sheet glass will continue to be used, mainly in thickness of 1/8" and less.
Side-On Pressure is what is felt on the sides and top of an object as the blast pressure wave envelops and passes over and around it. It is a term that is used when bomb blast testing fragment retention film.
A sill is the horizontal structure that supports the upright portion of a window frame.
Solar Heat Gain Coefficient
Solar Heat Gain Coefficient (SHGC) is the fraction of solar radiation admitted through a window, door, or skylight, either transmitted directly and/or absorbed, and subsequently released as heat inside a home. The lower the SHGC, the less solar heat it transmits and the greater its shading ability. It is a term that is used to evaluate the performance of a sun control window film such as 3M’s Prestige Series.
Spandrel Glass panels are heat strengthened or tempered glasses with a ceramic frit color permanently fused to one of the surfaces. Glass in spandrel areas is not subject to corrosion as are some other spandrel materials. Pleasing aesthetics and economies can be obtained using a single framing system for an entire wall. Glass spandrel panels can also save energy when insulation is placed behind them.
Standoff Distance is the distance you are from a blast. Generally speaking, the further you are from a blast, the better your opportunity to survive. Each site should be evaluated to assess its structural strength, window frame type and attachment, and glass type to determine which style of film application would be most appropriate to withstand the blast at a given distance. It is a term that is used when bomb blast testing fragment retention film.
Tempered Glass is fabricated by subjecting annealed glass to a special heat-treating process. The most commonly used process is to heat the glass uniformly to approximately 1,150° F, and then rapidly cool it by blowing air uniformly onto both surfaces simultaneously. The cooling process locks the outer surfaces of the glass in a state of high compression and the central portion, or core, in compensating tension. The color, clarity, chemical composition, and light transmission characteristics remain unchanged. Likewise, compression strength, hardness, specific gravity, expansion coefficient, softening point, thermal conductivity, thermal transmittance, and stiffness are unchanged. The only physical property that changes is tensile or bending strength. Under uniform loading, tempered glass is about four times stronger than annealed glass of the same size and thickness, and is thus more resistant to thermally induced stresses, cyclic wind loading, and hail stone impacts. When broken, tempered glass breaks into a multitude of small fragments of mostly cubical shape. Therefore, it qualifies as a safety glazing material under the criteria of Federal Standard 16 CFR 1201 and the American National Standards Institute (ANSI) Z97.1, when so labeled and certified. Spots or blotches may, at times, be visible on tempered glass, especially when viewed through polarizing lenses or in certain types of reflected light. The intensity will vary with lighting conditions and viewing angle. This is caused by the strain pattern induced during the cooling stage and is not inherently a cause for rejection. 3M’s Safety & Security Window Films can turn standard glass into safety glazing by most local codes. Your 3M dealer can supply code enforcement with the appropriate testing.
All glass absorbs energy when exposed to solar radiation. Tinted glass absorbs more energy than clear glass. Thermal stress occurs when there is a temperature differential between center of glass and its shaded edges. The ability of the glass not to break from thermal stress is determined by its edge strength. Thermal stress is why an end-user should consult a window film professional prior to making any window film decision. 3M Company provides a warranty against thermal stress in many situations so be sure to ask your 3M dealer about applicable coverage.
Tinted / Heat Absorbing Glass
Tinted or Heat Absorbing Glass is made by adding various colorants to the normal, clear glass batch to create the desired color. The four colors available by the float process are bronze, gray, green, and blue. Visible light transmittance will vary from 14% to 83%, depending upon color and thickness. The color density is a function of thickness and increases as the thickness increases. (Visible light transmittance will decrease as thickness increases.) Tinting reduces the solar transmittance of glass, has little effect upon solar reflectance, and hence increases solar absorption (heat). This explains why heat strengthening or tempering is sometimes required for the thicker tinted glass. Adding a metallic coating also has the same effect on thinner glass. Films such as 3M’s Night Vision Series can turn clear glass into tinted glass and provide the associated energy benefits.
TNT Equivalence is the quantity (Ib / kg) of an explosive material expressed in terms of the equivalent mass of TNT required to generate similar blast values. It is a term that is used when bomb blast testing fragment retention film.
Total Solar Absorption
Total Solar Absorption is the ratio of the total amount of solar energy that is absorbed by glass compared to the amount of total solar energy that hits the glass. This solar energy is neither transmitted through the glass nor reflected back out into the atmosphere. The use of window film can affect this.
Total Solar Reflectance
Total Solar Reflectance is the ratio of total solar energy which is reflected outward by glass compared to the total amount of solar energy falling on the glass. The use of window film can affect this.
Total Solar Transmittance
Total Solar Transmittance is the ratio of the amount of total solar energy in the entire solar wavelength range that passes through glass compared to the amount of total solar energy falling on the glass. The use of window film can affect this.
Transmissivity is the amount of radiant energy transmitted from a radiating object through the atmosphere to a target after reduction by atmospheric absorption and scattering.
U-Value measures the heat transfer that occurs through the inside and outside surfaces of glass. The U-Value is a function of temperature and is expressed in BTUs per square foot per hour per degree Fahrenheit (BTU / sq. ft. / hr. / F°). Better insulation systems, including insulating window film, have lower U-Values.
Ultraviolet (UV) is the damaging portion of the solar energy spectrum that causes fading and deterioration to fabrics, furniture, and furnishings. (Please note that there are other factors that contribute to furniture fade.) UV rays also age skin and cause skin cancer. Many 3M window film products block out up to 99.9% of the sun’s damaging UV rays.
Ultraviolet Inhibitors are chemical and material elements added to products such as window film and lotions to block and/or filter out varying amounts of harmful UV rays.
Ultraviolet Transmittance is the ratio of the amount of total UV solar energy that passes through glass compared to the amount of total UV solar energy that falls on the glass. The use of window film can affect this.
Visible Light Reflectance
Visible Light Reflectance is the percentage of total visible light that is reflected by glass and that can be seen. The use of window film can affect this.
Visible Light Transmittance
Visible Light Transmittance is the ratio of the total amount of visible solar energy (usually called light) that passes through glass compared to the total amount of visible solar energy that falls on the glass. The use of window film can affect this.
A wet glaze installation is the application of silicone sealant or similar liquid-state material around the perimeter of the glass to bond the film to the glass to the window frame. A wet glaze attachment system such as 3M’s Impact Protection Adhesive augments the performance of 3M Safety & Security Window Film.
Wired Glass is produced on the same equipment as figured / pattered glass. A welded wire netting or parallel wires are introduced into the molten glass just before entering the rolls to embed the wire into the glass. Patterned wired glass has a pattern on one or both sides and is sometimes called "rough" wired glass. Polished wire glass is produced by grinding and polishing rolled wired glass blanks. Tinted / heat absorbing wired glass is available only as an import. The heat absorbing characteristic in conjunction with the normally poor cut edges and the wire netting can cause a high rate of breakage from thermal stress, especially in non-vertical applications. The major uses of wired glass are in institutional buildings and fire rated windows and doors. All wires must be completely embedded in the glass. Some misalignments of the wires may be noticeable, but this is not considered cause for rejection. Wired glass cannot be tempered. Wired glass is being phased out in many applications due to the associated risks.