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Why Openness Doesn’t Matter

By Ali Fisher, Product Strategy Manager

Mermet Corp.

From aesthetic contribution and improved UV protection, to energy efficiency, heat control and glare reduction, modern solar shade fabrics offer numerous benefits to the design and function of space. However, despite the varied dividends of these fabrics, specifiers have traditionally focused attention on the Openness Factor (OF).

Openness Factor, which refers to the percentage of holes in a sunscreen fabric’s construction or weave, directly relates to the amount of light that passes through the fabric. For years, OFhas been used as a source of assessmentinfabric mills serving the window shade industry and remains the most widely adopted preliminary measurement most architects and designers useto qualify fabric selection. But times are changing. Newer, more objective, repeatable fabric testing standards and measurements are available. OF, on its own merit, serves as a subjective gauge for quality of view-through and UV blockage. OF cannot determine visibility, glare and thermal control by itself and should not be the primary focus of the application. Today there are several metrics that when combined with OF tell a much more compelling story. These metrics, to name a few, include Solar Heat Gain Coefficient, or G Value; Light Transmission Values (Tv); and Solar Reflection (Rs). Each installation has a diverse set of important circumstances that should be taken into consideration. From color variables to elements of performance and health factors to energy and sustainability, if architects, designers and specifiers prioritize application goals, OF matters much less.


Light and color go hand-in-hand. The variation in colors originates from the way solar radiationand visible light are reflected and absorbed by an object. In addition to enhancing the overall aesthetics of a space, color is a vital factor in specifying solar shade fabrics as it has a direct impact on solar heat gain, glare and work space productivity.

Light color fabrics provide high levels of visible light transmission (Tv) and regardless of openness, can reduce cooling loads more effectively than dark counterparts. Additionally, light color fabrics help preserve levels of natural light, which reduces the need for artificial lighting. There are some disadvantages of these fabrics to consider as well. As a result of its reflectivity, light color fabric can cause glare and create visual discomfort or can interfere with street side aesthetics.

Dark color fabrics absorb light, reduce visible light transmission and improve transparency during daylight hours. Aesthetically, darker color shade fabrics also “meld with the” glazed components of a building, becoming “invisible” from the interior and exterior. Dark fabrics can, however, absorb solar heat and contribute to thermal discomfort. Dual color fabrics – those that feature both light and dark colors – can provide superior thermal comfort and excellent natural daylighting for window shade applications.


According to the U.S. Department of Energy (DOE), “Commercial buildings represent just under one-fifth of U.S. energy consumption, with office space, retail space, and educational facilities representing about half of commercial sector energy consumption.”[i] The DOE also notes that the “top three end uses in the commercial sector are space heating, lighting and space cooling, which represent close to half of commercial site energy consumption.”[ii]

As building owners realize increased challenges to reduce rising energy costs and energy consumption, architects and designers are tasked to find more energy efficient, sustainable product solutions. When other fabric performance metrics are considered, solar shade fabrics can reduce energy consumption and contribute energy efficiency.By decreasing heat gain and contributing to natural day lighting, solar shade fabrics lower the energy used by artificial lighting, thus lessening overall heating and cooling costs as well as lessening the level of investment in light fixtures.


When blueprinting energy-efficient construction, architects and designers often consider solar variability.The variation of the sun’s position from day to day, season to season and by geographic locale, solar variability helps builders determine the amount of light protection needed for the structure.

Automated window shades also have the power to effectively manage daylight and enhance energy performance by adjusting to solar variability. Many sun control systems can adjust to the angle of the sun dependent on the location and orientation of the building, which enables the most advantageous placement of the shading system. Window shading arrangements that can automatically adjust to changing weather conditions and privacy at various times of the day (early morning or evening, for example) are also feasible. When used in conjunction with high-performing fabrics, the ability to increase daylight usage, enhance worker productivity, reduce eyestrain caused by glare, and improve thermal comfort, is all the more powerful.

By integrating the controls of automated shades into building systems, builders allow for a central control point. In addition to streamlining operations, integration makes it possible to synchronize shades with HVAC, fire and lighting control systems, further improving the building’s overall efficiency.


In the age of the green architecture movement, product lifecycle is often more important than openness for specifiers. Environmentally responsible building materials offer increased benefits to both the building owner and occupants including reduced maintenance or replacement costs over the life of the building, energy savings, improved occupant health and enhanced productivity and increased design flexibility. Today, fabrics that are Cradle to CradleSM[iii]certified, contain recycled content or are recyclable and are readily available in a wide range of performance levels, and openness factor.

Recently, fabrics made from recycled materials – a combination of post-industrial and post-consumer plastic waste – have been introduced to the market. In comparison to virgin polyester, a common material used for some window shading fabrics, the materials used to create these fabrics reduce energy consumption by more than six percent, water consumption by nearly 50 percent, and greenhouse gas emissions by more than 34 percent.


With the Environmental Protection Agency (EPA) ranking indoor air pollution among the top five environmental dangers, indoor air quality is an increasingly common challenge in the United States. In both homes and commercial buildings, this is often attributed to volatile organic compounds (VOCs), which can be found in anything from paint, flooring and cleaning products to furnishings and window fabrics. Additionally, the health effects of VOCs vary greatly but some risks of “exposure to elevated levels of VOCs may cause irritation to the eyes, nose, and throat. Headaches, nausea, and nerve problems can also occur.”[iv] Taking into consideration that the average American spends more than 90 percent of their time inside, VOCs and their impact on indoor air quality are of the utmost importance.

Manufacturers are working diligently to address indoor air quality concerns and develop and produce low VOC products. Several certifications are available to help specifiers make informed product selections. Once the product passes tests for indoor pollutant emissions it receives GREENGUARD® certification.

Fabrics that are RoHS (Restriction of Hazardous Substances) compliant are also a critical factor in the health and safety of the occupants. RoHS-compliant fabrics have been tested and rated for safe levels of heavy metals such as lead, mercury, cadmium, hexavalent chromium, PBB (polybromiated biphenyls) and PBDE (polybrominateddiphenyl ether).


Architect Richard Rogers once said, “My passion and great enjoyment for architecture, and the reason the older I get the more I enjoy it, is because I believe we - architects - can effect the quality of life of the people.” Buildings, after all, are made for the people who occupy them. There is not necessarily a singular factor that makes a product right for specification or application. Each component of a building weaves together with the other to create a fabric that allows occupants to heal, learn, work, live and create in beautiful, healthy and environmentally responsible spaces.

About the Author:

Ali Fisher joined Mermet in 2010and manages fabric development, testing and certification for the company. Herbroad experience in fabric fenestration testing and data analysishave contributed to the creation of several award-winning high performance sunscreen fabrics for Mermet.

[i] U.S. Department of Energy (DOE); Buildings Energy Data Book;

[ii]U.S. Department of Energy (DOE); Buildings Energy Data Book;

[iii]Cradle to CradleCertifiedCM is a certification mark of MBDC.