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Solar & Optical Properties


A market leader in solar protection for nearly 40 years, Mermet screen fabrics use a combination of high performing Enduris® fibreglass core yarn and polyester to minimise heat and glare.



What are Solar & Optical Properties?

Solar protection takes into account thermal and optical factors, which allow us to measure the solar protection performance of a fabric. Thermal factors relate to the amount of solar energy (heat) penetrating the fabric and provides a guideline as to how well the fabric will perform in keeping the inside warm in winter and cool in summer.


Optical factors relate to the amount of light a fabric will let through. Natural light is necessary for the human body to function, yet glare needs to be controlled and eye sight needs to be protected from harmful UV rays. Mermet fabrics protect against both heat and glare. 


The solar & optical properties (also called fenestration data) of each Mermet fabric can be found in the downloadable technical data sheets.

Thermal Factors - Fabric

Thermal factors include values such as Solar Transmittance (Ts), measuring the proportion of solar energy transmitted through the fabric, Solar Reflectance (Rs), measuring the proportion of solar radiation reflected by the fabric and Solar Absorptance (As), which measures the proportion of solar radiation absorbed by the fabric.


As a general rule, a high-performing, solar protection fabric has low Ts and As values, while it performs high in the Rs value, reflecting most of the solar energy. Solar radiation is always partially transmitted through, absorbed or reflected by the fabric.  The sum of all 3 equals 100.   i.e. Ts + Rs + As = 100% of solar energy.

Currently over 40% of emissions of greenhouse gases are released by building heating and air conditioning systems. In order to avoid irreversible climate change, it is necessary to reduce this output by improving the thermal performance of buildings through high performing Mermet fabrics.


Thermal Factors - Fabric & Glass

There are also a few other thermal factors to consider, which relate to the fabric’s thermal properties when combined with glass. The g-value is a measure of the total solar energy transmittance calculated using either EN 13363-1A1 (2007) or ASTM E903-96 standards.  A low number means better performance against solar heat build-up.

The Solar Heat Gain Coefficient (SHGC) shows how effective a fabric is at filtering the heat from solar radiation by measuring the window’s (fabric and glass) ability to transmit solar energy into a room.  The SHGC  is commonly referred to as g-tot.  SHGC/g-tot is a calculation of the solar protection device (fabric) and the glazing (CL-S/DG). The lower the g-tot value, the greater its ability to insulate against solar heat build-up.

The test data in Mermet’s downloadable solar and optical data sheets has been supplied using the following glazing types:


CL-S (EN14501 glazing type A)

  • Clear single glazing (4mm float) With a g-value of 0.85

DG (EN14501 glazing type C)

  • Double glazing (4mm float + 16mm space + 4mm float) with low emissivity coating in position 3 (outer surface of the inner plane), space filled with argon.  With a g-value of 0.59


Optical Factors

Natural light is essential to sustain human life and it governs a number of endocrinal functions, as well as regulates sleep and the body’s water balance. It also improves the working conditions experienced by employees and therefore increases productivity.


The following optical factors need to be considered when choosing a high-performance Mermet sunscreen fabric. Visible Transmittance (Tv), which measures the percentage of visible light coming through the fabric that can be seen by the naked eye, is related to the amount of light (brightness) a person receives through a glazing system. Visible Light Reflectance (Rv) measures the percentage of visible light reflected by the fabric to the outside of the building. The higher the number the more visible light is reflected. While the Openness Factor (Of) measures the proportion of holes in a woven fabric, therefore determining the degree of visibility and heat and glare control that the fabric offers, the Ultra Violet Transmittance (Tuv) factor measures the value of ultraviolet light going through the fabric.


Mermet fabrics have excellent glare control properties due to their various openness factors and weaves and can filter up to 95% of UV rays.

A new standard in solar protection

A new performance standard is being set by Mermet’s unique, patented KOOLBLACK™ Technology, which increases the energy efficiency of dark coloured sunscreen fabrics to levels comparable with light colours. 

KOOLBLACK™ delivers reduced cooling costs and improved comfort, with the glare control and view-through of a conventional dark screen fabric.

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