Frequently Asked Questions

  1. What is low-E glass (low-emissivity coated glass)? How many types of low-E glass are on the market? Is all low-E glass the same?
  2. Currently, the industry offers low-E on both the #2 surface and the #3 surface. On which surface would you recommend applying the coating to achieve the best solar performance?
  3. What is the difference between heat-strengthened (HS) and fully tempered (FT) glass? How do I determine which is needed for my project?
  4. What are the important values to consider when specifying glass for my project? Can you assist me with writing a glass specification?
  5. What is the difference between U-factor, U-value, and R-value?
  6. What is the difference between SHGC (Solar Heat Gain Coefficient) and SC (Shading Coefficient)?
  7. Should I use an argon- or an air-filled IG unit?
  8. How do I order samples of your glass?
  9. What is the availability of your products? What is the lead time?
  10. Where can I find a fabricator for SunGuard products?
  11. How can I earn LEED credit by using SunGuard products?
  12. Does Guardian supply hurricane-rated glass?
  13. Is laminated glass available from Guardian? Can it be obtained with low-E or other high performance-coatings?
  14. What is roll or roller wave distortion?
  15. What is a strain pattern?
  16. Does Guardian supply spandrel glass? How do I get my spandrel glass and vision glass to match in appearance?
  17. Does Guardian supply fire rated glass?
  18. How much does your glass cost?


  1. What is low-E glass (low-emissivity coated glass)? How many types of low-E glass are on the market? Is all low-E glass the same?
    Low-E glass refers to glass with a low-emissivity coating. It reduces heat gain or loss by reflecting long-wave infrared energy (heat) and therefore, decreases the U-value and solar heat gain, and in doing so, improves the energy efficiency of the glazing. Because of its relative neutrality in appearance and energy efficiency, low-E glass is widely used in residential and commercial buildings and is expected to continue to increase in usage in the coming years.

    Based on how it is manufactured, low-E glass can fall into two categories: pyrolytic deposition (hard coat) and vacuum deposition (sputter coating) low-E. The difference between the two is that the pyrolytic deposition method applies various metals to molten glass during the float glass manufacturing process. Vacuum deposition, on the other hand, applies various metals off-line in a large vacuum chamber. Pyrolytic coatings have higher solar heat gains and U-values and may not meet energy codes. They also can be less crisp in appearance compared to sputter coatings. Sputter coatings are offered in a wide variety of color and performance options, including post-temperable versions, and can meet and exceed energy code requirements.

    Guardian Industries manufactures SunGuard brand post-temperable sputter coatings at multiple locations in the U.S. and Europe. The SunGuard coatings are sputter coatings, not pyrolytic.

  2. Currently, the industry offers low-E on both the #2 surface and the #3 surface. On which surface would you recommend applying the coating to achieve the best solar performance?
    Most commercial or residential buildings in the U. S. are glazed with the low-E coating on the #2 surface for the maximum benefit in reducing heat gain to the interior of a structure. Reducing solar heat gain in the summer is more important for commercial buildings than increasing solar gain in the winter because the cost to air-condition a building is much higher than its heating cost. Low-E on the #2 surface reduces solar heat gain to the building’s interior. However, low-E is often used on the #3 surface when a tinted or coated outboard lite is used to provide even greater energy savings.

  3. What is the difference between heat-strengthened (HS) and fully tempered (FT) glass? How do I determine which is needed for my project?
    Heat-strengthened (HS) glass has been subjected to a specifically controlled heating and cooling cycle, and is generally twice as strong as annealed glass of the same thickness and configuration. HS glass must achieve a residual surface compressive (RSC) level between 3,500 and 7,500 PSI for thickness up to 6mm, according to ASTM C 1048. It has a greater resistance to thermal loads than annealed glass and when broken, the fragments are typically larger than those of fully tempered glass and initially may remain in the glazing opening.  Heat-strengthened glass is not a safety glass product as defined by building codes. It is intended for general glazing, and is usually the choice for commercial applications where additional strength is desired to withstand wind load and thermal stress, but the strength of tempered glass is not necessary or required by building safety codes. HS glass can’t be cut or drilled after heat-strengthening and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure.

    Tempered glass is approximately four times stronger than regular annealed glass of the same thickness and configuration. Its residual surface compressive (RSC) level must exceed 10,000 PSI for thicknesses up to 6 mm per ASTM C 1048.  When broken, it usually breaks into many relatively small fragments, which are less likely to cause serious injury in most applications. Tempered glass is often referred to as “safety glass” because it meets the requirements of various code organizations for safety glazing. This type of glass is usually intended for sliding doors, storm doors, building entrances, bath and shower enclosures, interior partitions and other uses requiring superior strength and safety properties. Tempered glass cannot be cut or drilled after tempering, and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure.

    It is important to note that the heat-treating process creates optical distortion that can be reduced but not eliminated. Guardian recommends that the glass manufacturer or fabricator be consulted and mock-ups be viewed and approved whenever possible.

  4. What are the important values to consider when specifying glass for my project? Can you assist me with writing a glass specification?
    Glass specifying can be a very complicated and time-consuming process. It starts from the fundamental question: What is the building’s overall function and design purpose, and what role can glass play to achieve the design objectives? Several key considerations include, but are not limited to, aesthetics, light transmission, energy performance requirements and codes, safety requirements and codes, etc. The Glass Association of North America’s (GANA) “Specifiers Guide to Architectural Glass” is a good reference.

    Guardian has developed a Product Performance Comparison Tool to assist in comparing the performance data for SunGuard Advanced Architectural Glass products. This tool will also generate a short-form specification. We are happy to answer your questions and provide specific project assistance as well. Please click here to contact us.

  5. What is the difference between U-factor, U-value, and R-value?
    U-factor and U-value are interchangeable terms referring to a measure of the heat gain or loss through glass due to the difference between indoor and outdoor air temperatures. U-factor or U-value is also referred to as the overall coefficient of heat transfer. A lower U-value indicates better insulating properties. The units are Btu/(hr)(ft2)(°F).

    R-Value equals a measure of the resistance of the glazing to heat flow. It is determined by dividing the U-value into 1, (R-value = 1/U-value). A higher R-value indicates better insulating properties of the glazing. R-Value is not typically used as a measurement for glazing products. Both U-value and R-value are a measure of resistance to heat flow and are referenced here to help understand U-value.

  6. What is the difference between SHGC (Solar Heat Gain Coefficient) and SC (Shading Coefficient)?
    The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 1/8" (3.1 mm) uncoated clear glass has an SHGC of approximately 0.86, of which 0.84 is direct gain (solar transmittance) and 0.02 is indirect gain (convection / re-radiation).

    The Shading Coefficient (SC) is a measure of the heat gain through glass from solar radiation. Specifically, the Shading Coefficient is the ratio between the solar heat gain for a particular type of glass and that of double-strength clear glass. A lower Shading Coefficient indicates lower solar heat gain. For reference, 1/8" (3.1 mm) clear glass has a value of 1.00 (SC is an older term being replaced by the SHGC).

    In either case, a lower number indicates improved solar control over the 1/8" clear glass baseline. With a long air-conditioning season, it is most important to reduce solar gain and therefore reduce air-conditioning loads.

  7. Should I use an argon- or an air-filled IG unit?
    Insulating Glass Units (IG Units) can be made with air or other gases between the two lites of glass. While air itself is a good insulator, filling the gap between the glass panes with a lower-conductivity gas such as argon can improve performance by reducing conductive and convective heat transfers. This phenomenon results from the fact that the density of the gas is greater than the density of the air. Air-filled IG units are commonly used in commercial applications. However, an argon-filled IG unit sometimes might be required in order to meet specific requirements and energy codes.

    The use of a less conductive gas in an IG unit has insulating benefits but may come at a higher initial cost compared to an air-filled IG unit. There are also concerns about maintaining the gas fill levels over time. Argon permeation is greater than air for most IG sealants, which can result in negative pressure in the IG air space. Argon-filled units also cannot use breather tubes for high-altitude applications.

  8. How do I order samples of your glass?
    You can easily obtain SunGuard samples in 10x15cm or 30x30cm sizes, or you can order architectural sample boxes by filling out our online request form.

  9. What is the availability of your products? What is the lead time?
    Guardian’s SunGuard brand coated glass offers the architect or designer the largest selection of post-temperable sputter coated products. SunGuard Advanced Architectural Glass products are available through our nationwide independent SunGuard Select Fabricators network so there is sure to be one near your project.

    Since SunGuard coated products are post-temperable, they can be cut, heat-treated, tempered, laminated and even bent at the Select Fabricator’s facility. This means shorter and more consistent lead times on new and replacement glass. Many SunGuard coated glass products are maintained in inventory by Select Fabricators and are readily available for your project. Contact your local independent SunGuard Select Fabricator for specific product availability and lead times.

  10. Where can I find a fabricator for SunGuard products?
    All independent SunGuard Select Fabricators are trained and certified by Guardian in the proper procedures and practices for the fabrication of Advanced Architectural Glass. Click here to find a Select Fabricator that meets your project’s needs.

  11. How can I earn LEED credit by using SunGuard products?
    Guardian supports the Leadership in Energy and Environmental Design (LEED) rating system and is a proud member of the U.S. Green Building Council (USGBC), a coalition of building industry leaders who promote and create environmentally responsible structures. The USGBC’s LEED system awards points for using recycled materials, reducing energy use (both during and after construction), and adopting other methods to minimize environmental impact –while improving the working environment as well.

    Using SunGuard Advanced Architectural Glass can help you earn up to 20 total points in four of the six LEED categories, including transportation.

    For complete details on all the ways SunGuard Advanced Architectural Glass can help you earn LEED points, click here to download our LEED brochure.

  12. Does Guardian supply hurricane-rated glass?
    It is important to note that glass is only a component of the overall configuration that meets hurricane-resistant codes. Many other components contribute to the performance of the glazing, such as frame, silicone, anchorage, hardware, etc. Thus, the complete glazing system must meet the specified hurricane test protocol to be considered a certified hurricane-resistant product. Guardian offers a variety of SunGuard coated glass products that can be laminated, such as SuperNeutral 68, and that meet hurricane codes when installed into an approved glazing system. For more information, please click here.

  13. Is laminated glass available from Guardian? Can it be obtained with low-E or other high-performance coatings?
    Guardian produces architectural laminated glass in a full array of thicknesses and sizes, and many types of SunGuard Advanced Architectural glass can be laminated. For your special project and applications, please click here.

  14. What is roll or roller wave distortion?
    The process of heating float glass to a level of soft pliability, then rapidly cooling it, will always cause optical distortion to some degree. This is the case for heat-strengthened and fully tempered glass. One common form of optical distortion is roller wave. During the heating process, glass will sag very slightly between the carrier rolls that transport the glass through the furnace. After heating, the glass passes through the quench, which “freezes” the glass, creating the compression and tension that provides either heat-strengthened or fully tempered glass. However, this process can also result in a slight deviation from optically flat glass, usually seen as ripples or roller wave. Glass thickness and size affect the amount of distortion: Generally, the thicker the glass, the less deviation from flatness, while larger glass sizes may also appear to have more distortion.

    To reduce optical distortion, many issues must be considered in optimizing the heat-treating process. For example, the conveyor system, furnace temperature uniformity and the quench design will all affect the optical quality of heat-treated glass. Independent SunGuard Select Fabricators must demonstrate during certification they can produce heat-treated glass to commercial standards. However, because of the nature of roller wave distortion, it can only be reduced, not totally eliminated.

  15. What is a strain pattern?
    Strain patterns are also called quench marks. The terms describe an optical phenomenon inherent to heat-treated (heat-strengthened or fully tempered) glass that appears as a series of light and dark areas. The strain pattern is especially visible when viewed at an angle of (45º-60º) to the glass surface, and it is more noticeable when you are wearing polarized sunglasses. It is not a defect but a characteristic of heat-treated glass.

  16. Does Guardian supply spandrel glass? How do I get my spandrel glass and vision glass to match in appearance?
    Guardian does not manufacture spandrel glass directly, although SunGuard coatings can be an important part of your spandrel glass solution.

    Generally speaking, matching spandrel glass to vision glass that’s either high-transmittance or low-reflection can be difficult. The degree of color and visual similarity of a building’s vision and spandrel glass can vary greatly depending on several factors: light transmission, time of day, sky conditions and interior shading.

    Higher light-transmitting glass will require more complementary spandrel glass, while lower transmitting/higher reflecting glass can provide a better matching spandrel. Whatever the project, we always recommend a full-sized outdoor mockup be constructed to provide the most accurate view of vision and spandrel glass.

    We recommend that you contact Guardian or consult an independent SunGuard Select Fabricator for information about spandrel glass capability.

  17. Does Guardian supply fire rated glass?
    Guardian does not produce fire rated glass.

  18. How much does your glass cost?
    Guardian Industries is a fully integrated, primary glass manufacturer with many float glass lines and coaters around the world. However, we generally do not do the final fabrication of the insulated glass unit. We supply our coated glass to our network of SunGuard Select Fabricators, who then fabricate the glass as required by the order or specification. Guardian recommends that you contact an independent SunGuard Select Fabricator and/or a local glazing contractor to assist you with cost estimates for fabricated and installed glass products.

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