Multi-pane insulating glass

from Wikipedia, the free encyclopedia

Insulating glass (MIG), also known as heat-insulating glazing or double glazing referred to is an at least two panes of glass composite device for windows and other glazings. There is a cavity between the panes, which is sealed gas and moisture-tight and is used for sound and heat insulation . Forerunners were double glazing without air exclusion, composite windows and double single glazing for box or winter windows .

Exemplary structure of a 2-pane or 3-pane thermal insulation glass (dashed). The butyl seal of the spacer is also referred to as the 1st sealing stage and the outer polysulphide seal as the 2nd sealing stage.
The sun protection coating on the inside of the outer pane of glass reflects the infrared radiation and reduces the heating of the building in summer.
A Low-E coating (not shown here) on the outside of the inner pane reflects the thermal radiation back into the room and significantly improves the insulation value of the glazing.

In the first decades since the appearance of multi-pane insulating glass (1950s to 1970s), the Thermopane brand was widely used in the German-speaking world. At times the name became synonymous with double-pane insulating glass. As a Product and the terms climate protection glass , thermal glass , insulating glass or thermal insulation glass used.

Expressions such as solar glass , privacy glass , break-resistant glass or soundproof glass typically refers to a multi-pane insulating glass with special additional features, although a single flat glass construction, this may have also.

History in the Federal Republic of Germany

In contrast to warmer climatic zones in Central and Northern Europe, the focus of heat-insulating windows is less on reducing the required cooling energy (high operating costs for air conditioning systems) and more on making substantial savings in heating energy for buildings. This results in very different regional requirements, structural guidelines and implementations for the glass structures of the windows within Europe. From 1950 to 1978 single-glazed windows as well as box and composite windows with two single panes dominated in the FRG. After a Thermal Insulation Ordinance (WSchVO) came into force in 1977, the use of single glazing for residential buildings was legally permissible until 1978. From 1978 insulating glass windows increasingly came onto the market. (Double) insulating glazing was typically installed between 1975 and 1994. From 1995, the coated thermal insulation glass (Low-E) and the filling with thermally insulating gases (argon, krypton, occasionally also xenon) became the standard. In the meantime, triple thermal insulation glass is mostly produced and used for new windows in Germany, and quadruple constructions are also being used in isolated cases.

The Europe-wide CE marking of insulating glass, based on the harmonized product standard DIN EN 1279, replaced the national standard DIN 1286 previously valid in Germany in 2007. The Gütegemeinschaft Multi-pane insulating glass places additional requirements on multi-pane insulating glass as well as on the quality and properties of the primary products that go beyond this product standard. There are similar activities for quality assurance in many European countries, whereby, due to the different climatic requirements for this building product, in practice very different requirements are understood and implemented in some cases.

Mode of operation and structure

Triple insulating glazing in plastic and wooden window profiles
Triple insulating glazing in the wooden window frame

In contrast to other types of heat insulating glazing, insulating glazing is an independent system that does not require a surrounding frame - usually a window sash. This is achieved by means of an edge bond that holds the individual panes of glass together at a distance and at the same time hermetically seals the space between the panes . Air (thermal conductivity λ = 26 mW / (m K)) in the space between the panes has not been used for decades; instead, argon is the gas usually used here (λ = 18 mW / (m K)), and for some years that has been the case more expensive krypton (λ = 9.5 mW / (m · K)), which results in better thermal insulation, especially with narrow spaces between the panes, rarely also the even more expensive xenon (λ = 5.5 mW / (m · K)).

In order to minimize the heat conduction of an insulating glass pane, the space between the panes can be enlarged to over 20 mm when filled with air. As gases increase in volume, however, not only transfer heat by conduction , but also by drafts ( convection ), depending on the filler gas, the thermal insulation is effective from a pane distance of 14 to 16 mm (argon) or from 10 mm (krypton) the trapped gas worse again. To prevent this, another (third) pane of glass can be built into the insulating glass.

Insulating glass has a greenhouse effect . Glass panes are more permeable to the incoming solar radiation than to the infrared thermal radiation emitted from inside the room . The permeability for thermal radiation decreases with the number of glass panes and can be further reduced by a vapor-deposited metal layer per glass pane. The positive effect achieved at the same time worsens the possible solar heat gain, since it also reduces the energy transmittance (g-value). The total heat loss can be calculated using a formula, depending on the thermal insulation value (U-value), the degree of energy transmittance and the amount of solar radiation available ( radiation gain coefficient ). As a rule, if the sun is in a favorable position, a higher g-value (and a slightly worse and therefore higher U-value) is better. If there is little winter sun, the importance of the U-value is far higher than that of the g-value.

The heat losses of an insulating glass pane are mainly determined by the following factors:

  • Number and thickness of the spaces between the panes and the type of filling gas.
  • Number of panes of glass, as well as the coating of the panes of glass to reduce losses through thermal radiation (the thickness of the panes of glass has no influence).
  • Thermal conductivity of the edge seal and the glass retaining strips (installation situation on the pane edge; see below).
  • Inclination angle of the insulating glass pane.
  • Solar radiation supply (south or north orientation, degree of shading, duration of sunshine in the heating season).

Gas filling

In the past, the space between the individual panes - the space between the panes (SZR) - was simply as dry as possible. For decades, the cavity has been filled with the better heat-insulating noble gases argon , krypton and occasionally xenon or mixtures of these gases. With the noble gases mentioned , the thermal conductivity of the insulating glass unit is not only significantly lower than with air, the distance between the panes can also be selected significantly smaller - a great advantage especially for heavy triple or multiple pane structures with more than one gas layer and for insulating glass units where e.g. B. for monument protection reasons, there are restrictions on the total thickness of the composite.

In the past, sulfur hexafluoride (SF 6 ) was used as the filling gas for soundproof insulating glazing, or a mixed gas made of argon and SF 6 was used for combined sound and heat insulation . Due to the very high global warming potential, SF 6 is no longer used in Central Europe, so other methods - such as the use of laminated glass - are used for this special requirement .

The gas pressure in the space between the panes generally corresponds to the air pressure at the production site of the insulating glass pane, but can be adapted to the air pressure and / or the temperature at the later installation location using different methods or aids (capillary tubes, mini-valves) in order to eliminate bulges and corresponding mechanical stresses to avoid in the glass. The difference in height between the production site and the installation site must not exceed certain values ​​in the case of hermetically sealed systems, depending on the size of the pane, as otherwise the edge seal or the glass panes will be subjected to inadmissible stress either at the time of production or at the later installation site. In the case of height differences of more than 1000 meters, special precautions must be taken and dimensioning issues to be clarified, especially with argon fillings: the larger the space between the panes, the smaller the pane formats and the stiffer (thicker) the individual panes of glass, the greater the risk that the Edge seal whose service life is reduced or leads to glass breakage. One speaks here of the climate load, which can be determined in special verification procedures. This applies in particular to the triple and quadruple glazing, as the sum of the space between the panes (SDR) is decisive for the climatic load. For conventional triple glazing with argon (cavity = 2 × 12 mm), edge lengths below 600 mm are considered problematic in the literature, with an cavity of 2 × 18 mm the minimum length would already be 900 mm, so that for small, well-insulating glass units With a high climate load, only thin pane units with krypton filling (cavity = 2 × 8 mm) or with an expensive xenon filling (cavity = 2 × 6 mm) are possible.

Edge seal

Aluminum spacers with widths of 10, 14 and 20 mm
The same spacers with a view of the cross section

The task of the edge seal is to hold the glass panes together mechanically at a certain distance and to prevent the gas filling from escaping and ambient air and moisture from penetrating.

At the beginning of the technical development of double insulating glass , a metallic spacer was soldered in between the two panes. Another method, as with vacuum insulating glass, was to heat the edge of the glass and at the same time to crank it in order to fuse the edge of the two panes of glass together in a gas-tight manner. These welded glasses were known under the brand names Gado and Sedo .

For decades, a two-stage bonded edge seal developed by Alfred Arnold in 1959 has been common. A 6 to 20 mm wide profile made of aluminum , stainless steel or plastic serves as a spacer . For a rectangular pane, either four individual profile strips are connected to one another via prefabricated corners or a continuous profile is bent at right angles at the corners and welded or glued at the joint. The resulting strip frame is placed between the two panes of glass and glued to them with a layer of polyisobutylene or butyl rubber .

The material of the edge profile and the polyisobutylene must seal the edge seal against filling gas, ambient air and water vapor. The frame made of spacer profiles is made slightly smaller than the glass panes, so that after the glass holder is glued in, a U-shaped joint remains between the glass edges. After the space between the panes has been filled with gas, this joint between the spacer, which is indented by about 3 mm and the protruding glass edges, is filled with paste-like polyurethane , silicone or special polysulphides .

In order to protect the sealants from the influence of UV radiation, insulating glass manufacturers usually require the side of the edge seal to be covered by a seam ("glass inset") or a glazing bead with a width of around 14 mm (as of 2014) . For facade elements that are exposed to UV light at this point, black silicone is usually used instead of butyl, polyurethane or polysulphide, which is, however, significantly more permeable to gas.

Incompatibilities between the sealants , which are used to seal the insulating glass pane in the window frame or to seal the joint between two panes, and the sealants in the edge seal are problematic . A migration of plasticizers or contact with harmful oils or other substances can take place here. Likewise, harmful interactions can also occur between the plastic material of the glazing blocks and the edge bond, in particular if the blocks contain styrene compounds . It is important to ensure that liquid joint seals such as silicone are not inserted so deep that they can no longer dry out in the rear areas. Instead, the joint should first be filled with tape .

The edge seal plays a decisive role in the function of the insulating glass pane, although a minimal diffusion of gases and water vapor through a bonded edge seal cannot be completely avoided. The thermal insulation value deteriorates slightly but continuously due to the slowly escaping filling gas: the binding specification for sealants is 90% gas filling with a maximum of one percent gas loss per year. With properly manufactured and sealed systems, however, significantly lower gas losses can be found in practice, so that a service life of 20 to 30 years can be assumed for insulating glass, with almost unchanged performance data. A desiccant from the family of silica gels or molecular sieves ( zeolites ) is placed in the spacer so that moisture that penetrates or that has already been trapped during production does not immediately accumulate as condensate in the space between the panes . Only when the desiccant has been used up can the inside of the pane fog up. A pane with permanent cloudiness is also known as a "blind pane".

Influence on the thermal resistance of the glazing

The edge seal significantly deteriorates the thermal insulation to be achieved for a gas-filled insulating glass pane. The heat transfer coefficient for insulating glass is specified as Ug value (g = glazing ) and, in contrast to the Uw value of the entire window (w = window), does not initially take into account the effects of the edge seal. A double insulating glass pane measuring 1 m × 1 m with a conventional spacer made of aluminum ( Psi value : 0.068 W / (m · K) and a Ug value of 1.2 W / (m² · K) has the same effect of the edge seal has a U-value of: (1 m² × 1.2 W / (m² · K) + 4 m × 0.068 W / (m · K)) / 1 m² = 1.5 W / (m² · K)

The impairment of the thermal insulation at the edge of the pane also leads to the condensation of water on the inner edge of the pane and mold formation on the sealant at low outside temperatures and high humidity in the living spaces . By using a thermally improved edge seal - the so-called " warm edge " with psi values from 0.03 W / (m · K) to 0.05 W / (m · K) - condensate falls depending on the psi value and room humidity only at lower outside temperatures or not at all. The latter is the case when the heat transfer resistance of the outer walls or certain cold bridges is lower than that of the glazing, so that the air humidity is reflected there.

Wavelength-selective coating ("Low-E")

Bodies radiate heat energy . This is known as emissivity . Metals have a significantly lower emissivity than glass in the relevant wavelength range (middle infrared approx. 2.5 ... 10 µm) ( thermos flask principle ). The Low-E coating (from the English word Low Emissivity ) is a thin metal or metal oxide layer applied to glass to reduce emissivity. The glass coated in this way is also called Low-E glass or LE glass . The coating of a low-E glass must be as transparent as possible for the incoming solar radiation, which results in a high total energy transmittance and no shifts in the visible light spectrum as with some sunglasses. Layers made of silver, copper or gold and tin oxide are suitable for this. The frequently used silver coating is embedded in oxide layers in the low-E coating, which increases transmission and durability. Layer thicknesses of 70… 180 nm are common.

The principle of the Low-E coating, which is usually applied by sputtering or pyrolytic coating (with higher demands on mechanical resistance), is not tied to the insulating glass pane. This also reduces the Ug value with single glazing. In the case of insulating glass, the Low-E coating is usually applied to the pane on the room side towards the space between the panes. The type of coating also determines, among other things, the total energy transmittance, the light transmittance LT (percentage of the continuous radiation range from 380-780 nm), the degree of light reflection (percentage of the externally reflected radiation range of 380-780 nm), the UV transmittance (percentage Proportion of the continuous radiation range of 280-380 nm) and the color rendering index Ra . Functional glasses such as sun protection glass or mirrored glass can be produced in this way.

The metal coating also dampens radio waves as a side effect. In the frequency range of modern cellular phones, attenuation of up to 30 dB is achieved; this corresponds to a shielding of up to 99.9%. Most trains are now equipped with metallised panes. If they are not already equipped with so-called intrain repeaters, which transmit the radio signals between antennas attached outside and inside, Internet access is only possible in the immediate vicinity of the base stations. Telephoning is subject to fewer restrictions due to the lower bandwidth and the lower frequencies in some cases.


The Ug values ​​of double insulating glass in 2020 will be around 1 - 1.1 W / m²K and of triple insulating glass between 0.5 and 0.6 W / m²K

In addition to conventional insulating glass, there are also special versions such as soundproofing , sunscreening or safety insulating glass. The technical difference between these and conventional insulating glass is primarily in the respective structure: With specially coated glasses and different gas fillings, significant advantages can be achieved.


Sound can be effectively dampened by using glass panes of different thicknesses . Due to the different thicknesses, the panes have different natural resonances, in the respective area of ​​which the sound insulation is greatly reduced (up to about 10 dB or more per pane). This resonance frequency (in Hz) is calculated by dividing 12000 by the glass thickness (in mm). If panes of different thicknesses resonate in different frequency ranges instead of the same, this prevents the “breaks” in the sound insulation curve from adding up. In the case of interfering noise with a lot of low-frequency noise (e.g. heavy road traffic), the reduced sound insulation in the area of ​​the natural resonances of the glass panes plays a subordinate role, as these are in the four-digit Hertz range for glass thicknesses of up to 12 mm . The frequencies are thus well above those of the most intense background noise.

For this purpose, special technical guidelines have been developed that are used, for example, as a basis for urban soundproof window programs on busy streets. There was a soundproof window program in Cologne from 1990–2007: "In addition, windows were often renewed due to the thermal insulation requirements in the meantime, which meant that increased noise protection could be achieved." In general, sound insulation class IV ( sound insulation value 40–44 dB according to VDI guideline 2719) is recommended.

Particularly thin thermal insulation glass

Especially when renewing windows in historic and listed buildings, the face width of window sashes, frames and bars should roughly correspond to the original windows. In the past, the thicknesses of the profiles were also adapted to the size of the window sash and the load resulting from the type of opening and the fittings used. Today's wooden windows are manufactured with a standard profile, which often reaches twice the width of some filigree historical profiles. With particularly small windows, the use of standard profiles can mean that there is hardly any space left for the glazing.

Specialized companies offer narrower window profiles especially for use in historical facades. However, due to the pane packages of 24 to 40 mm thickness that are common today, the window profiles must be designed so deep that when the window is viewed at an angle, the impression of very wide sash profiles is created again.

This is remedied by particularly thin insulating glazing. The smallest dimension of around 6 mm thick is achieved by double panes with a vacuum-sealed cavity . Double-glazed insulating glass is available in special designs from a total thickness of 10 mm (2-6-2, glass-space-glass in mm), with a thickness of 12 mm (3-6-3, Ug value 1.4 W / (m² · K)) is used. It is often possible to use these narrow glasses in existing historical window sashes by milling the glass rebate (putty rebate) wider.

For the production of new windows, which should visually approximate the historical model, particularly narrow (standard) profiles with the construction depth IV 58 are offered, which can be equipped with triple glazing. For example, 28 mm (3-10-2-10-3), 30 mm (3-10-4-10-3, Ug value 0.8 W / (m² · K)) or 31 mm (4- 10-3-10-4) thick thermal insulation glasses.


As a rule, insulating glass is installed in a frame in such a way that the pane does not touch the supporting frame directly at any point and a minimum distance ("glass clearance") of 5 mm between the edge of the insulating glass pane and the frame (glass rebate base) is maintained using glazing blocks. The glazing rebate base must be ventilated to the outside air in order to enable vapor pressure equalization. Penetrating seepage water must be able to run off. In Germany, DIN 18545 and DIN 18361 apply to the installation of insulating glass panes. However, there is no obligation to comply with these standards.

Structural glazing glass facades can consist of an almost continuous area of ​​insulating glass panes. Only interrupted by the pane joints that are glued with a sealant .

Essential glazing systems for insulating glass:

Dry glazing
The joint between the insulating glass pane and the frame is sealed with profiles made of elastic plastic; the frame corners of the sealing profiles can be welded or just butted.
Direct glazing
Also known as a glued disc . (Not to be confused with structural glazing ). Here the insulating glass pane is firmly glued into a frame in order to achieve a supporting effect. This means that the surrounding frame profiles can be made weaker (less load-bearing). This is particularly the case with plastic windows.
Wet glazing
The joint between the insulating glass pane and the frame is sealed using sealing compounds that cure permanently elastic after being introduced, for example silicone .
Single glazing are still mainly with the traditional window putty from linseed oil used. Most insulating glass panes must not be sealed with window putty, as the oil can damage the sealing materials of the edge seal.

Wet glazing without masking tape

Prior to the application of the sealant in the wet glazing at least three millimeters thick would be in accordance with DIN 18545 glazing tape to be put between the glass surface and the frame material. This is not done in the case of glazing without adhesive tape . While this is common practice, some insulating glass manufacturers advise against it.

Future developments

State of the art (2017) in Germany are triple glazing with a Ug value of around 0.6 W / (m² · K) to 0.8 W / (m² · K) and a thermally improved edge seal ( warm edge ). After three-pane glazing with xenon gas became uneconomical, four-pane glass (with wide spacers) with Ug values ​​of around 0.4 W / (m² · K) are now also manufactured in series in the area of ​​low-energy and passive house construction.
[Rough rule of thumb: A reduction of the U-value by 0.1 W / (m² · K) saves about 1.1 l of heating oil per m² and heating period , if the number of heating degree days is 3600 (average value in Germany for existing buildings) and the oil heating 75% Has efficiency

Thinner inner panes are currently being developed or launched to reduce weight (conventional triple glazing with 4 mm glass weighs 30 kg / m²), integrated photovoltaic elements, or electrically variable light and radiation permeability ( intelligent glass ). With the edge seal, the development is moving towards an all-plastic system, which facilitates the fully automatic production of insulating glass. Compared with conventional multi-pane insulating glass, when using toughened thin glass panes, in addition to saving weight, better thermal insulation values ​​can also be achieved. With a light transmission of 71%, the element structure with an outer 4 mm float glass pane, a 2 mm central pane and an inner 3 mm float pane weighs 22.5 kg / m² and has a Ug value of 0.6 W / (m² · K).

The design of windows is also changing due to increased requirements for thermal insulation . Real (glass-dividing) bars for dividing into several small glass fields are problematic because the poorer thermal insulation values ​​of the pane edge ( Psi value ) are all the more important, the better the thermal insulation values ​​(Ug value) of the panes. The thermal stress ( climatic load , see above) requires large-format panes or special gas fillings , especially with triple and quadruple glass. So that the Uf values (f = frame ) of the frame can keep pace with the Ug values ​​of the glass, the overall depth (thickness) of the window frame is increased and additional chambers with a heat-insulating insert are provided. In this way, Uf values ​​between 0.9 W / (m² · K) and 1.2 W / (m² · K) are achieved.

Vacuum insulating glass (VIG) was first manufactured at the University of Sydney in 1989. In 1996, Nippon Sheet Glass began commercial production under the Spacia brand . In 2013 a Ug value of 0.7 W / (m² · K) was achieved. In the approximately 0.2 mm wide space between the panes (SZR), many small, clearly visible spacers are attached in a grid-like manner to stabilize them against the external pressure. There is a clearly visible evacuation valve in one corner of the pane. The edge of the pane is sealed by means of a soldered-in metal strip. The resulting greatly deteriorated thermal insulation at the edge of the pane (= very high psi value) represents a thermal bridge , promotes the accumulation of condensation at the edges and significantly reduces the thermal insulation for the entire unit. So far, these panes have only been used for special applications, for example in listed windows, where often no installation space is available for standard insulating glass. Commercial production in Europe is not known until 2013.


Despite millions of uses, insulating glazing can be damaged under special conditions, which usually results from the failure of the edge seal.

The edge seal may leak after a long period of time. Water vapor diffusing into the space between the panes makes the insulating glazing 'blind' and vapor-deposited reflective metal layers can corrode.

With very large windows, special attention must be paid to the uniform blocking of both glass edges and the rigidity of the support in order to avoid tension in the glass, which can lead to leaks and breakage.

The creation of overpressure or underpressure in the space between the panes, which leads to the curvature of the panes, is also unfavorable. If the installation location is 200 m lower or 600 m higher than the manufacturer's works, pressure equalization measures are required. It is possible to introduce a corresponding positive or negative pressure into the space between the panes during production. Alternatively, the panes can be vented once at the installation site or equipped with venting devices (capillary tubes or valves ) which, if possible, do not lead to a dilution of the filling gas.

Sunlight also increases the pressure in the space between the panes. In the case of large panes, the curvature of the panes usually provides sufficient pressure relief. With smaller panes as well as with thick glass, a higher pressure arises in the gap, as these deform less flexibly. The excess pressure also increases with the width of the space between the panes, since the greater the volume of air is affected by heating and expansion. With the pressure, the stresses acting on the glass increase and thus also the risk of damage to the glass and edge seal (the middle pane (s) can be largely ignored when looking at it, the outer panes deform like a double-glazed pane with a correspondingly enlarged space between the panes). The deformation of the thinner pane also increases if the opposite pane is significantly thicker and stiffer.

Panes with triple or quadruple glazing are particularly affected, as the outer panes enclose an even greater volume of air here.

In order to rule out damage due to heating, an edge length of at least 60 cm is recommended for triple glazing with 4 mm thick panes and a space between panes of 2 × 12 mm (4/12/4/12/4). In the case of sound-insulating glazing with an asymmetrical structure of 8/18/4/18/4, the minimum edge length increases to 1 m, while it was only 45 cm with a previously common 4/16/4 structure. Smaller panes require a reinforced edge bond in combination with thermally toughened glass panes .


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Web links

Commons : Insulated Glass  - Collection of pictures, videos and audio files

Individual evidence

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  2. ↑ Saving more energy with new windows - September 2017 update of the study “In the new light: Energetic modernization of old windows” p. 3, Association of Windows and Facades (VFF) and Federal Association of Flat Glass (BF) (PDF; 795 kB).
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  7. DOW CORNING - Quality Manual for Insulating Glass
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  10. How monument protection works in window construction - renovation with a concept , BM online, November 2014
  11. Leaflet on material compatibility - material compatibility around insulating glass - insulating glass sealants, glazing sealants, blocks , Bundesverband Flachglas - wholesale insulating glass production, Veredelung eV, 6/2014
  12. ISOLAR - article on the edge seal with reference to the service life of 20 to 30 years  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. . PDF document, accessed November 7, 2012.@1@ 2Template: Dead Link /  
  14. Prof. Dr.-Ing. habil. Karl Gösele: Calculation of the sound insulation of windows, sheet 6, October 31, 1983. Publisher: Fraunhofer IRB Verlag, Fraunhofer Information Center Space and Building, Nobelstrasse 12, 70569 Stuttgart
  15. Municipal soundproof window program in Munich , September 2013 and August 2016
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  23. INTERPANE - design with glass; 8th edition. - Chapter 7 (p. 322) ( Memento of the original dated November 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . PDF document. Retrieved May 4, 2012. @1@ 2Template: Webachiv / IABot /
  24. Lighter triple ISO (thin glass). Retrieved December 3, 2017 .
  25. - First production by VIG 1989. Retrieved on Feb. 22, 2013.
  26. Information sheet pressure compensation , Flachglas (Schweiz) AG
  27. Franz Feldmeier: Climatic loads with triple insulating glass , laboratory for thermal building physics, Rosenheim University