Saflex® Solar interlayers - special high-visible-light-transmittance interlayers
Saflex® Solar interlayers are high-visible-light-transmittance, infrared (IR) radiation-absorbing interlayers designed to enhance solar heat gain performance in laminated glass compared to monolithic clear glass and laminates made with conventional polyvinyl butyral (PVB) interlayer. They have the capability to meet or exceed many regulations for laminated safety glazing when properly selected, laminated, and installed. The ideal solar product eliminates UV and NIR energy while allowing as much visible light transmittance as possible. Saflex Solar has the transmittance of a highly effective high-visible-light-transmittance solar product. Two options are available in the Saflex Solar range. Saflex Solar SG is our highest performing Solar PVB interlayer. Saflex Solar SH has a more color-neutral appearance and may be laminated with annealed glass in some applications.
Which one to use?
The decision to use either Saflex Solar SG or Saflex Solar SH is almost always driven by four technical glass design parameters: visible light transmittance, solar factor, the color rendering index, and solar absorptance of the exterior pane. Details of each parameter follow, along with their relevance.
- Visible light transmittance (VLT) is the fraction of the incidental light that is transmitted by the glass. The parameter is a measure for how much light is brought into the building, how clear the building occupants are able to see the exterior, and vice versa for people outside the building.
- The heating of a building through glass is driven by the solar energy transmittance or solar factor (g-value or SHGC) of the glazing. The solar factor is calculated as the sum of the solar direct transmittance and the secondary heat transfer factor of the glazing towards the inside, the latter resulting from heat transfer by convection and longwave IR radiation of that part of the incidental solar radiation that has been absorbed by the glazing. This parameter is important for the design of cooling and ventilation system in buildings and effects the comfort experienced by the users of the building.
- The color rendering index (CRI) is the change in color of an object as a result of the light being transmitted by the glass, where a value of 100 indicates no change. In most cases, a fairly natural color perception is desired.
- The solar direct absorptance is the difference between 100% and the sum of the solar transmittance and reflectance. The solar absorptance of the exterior pane is denoted here as αe,1. This value determines to a large extent how much a particular glazing heats up and is an important factor in determining if glass strengthening is required to avoid thermal stress breakage of the glass. A conscious decision regarding the need for glass strengthening for thermal stress reasons is typically taken for configurations having a solar absorptance of 50% or greater, although in some cases, strengthening may be required at lower absorptance values.
Configurations
To illustrate how choice of Saflex Solar affects these parameters, three examples are provided. The configurations are as follows, and are schematically depicted in Figure 1:
- Configuration 1: Basic (4-mm clear |0.76-mm interlayer| 4-mm clear)
- Configuration 2: Double skin façade -outer surface (10-mm low iron | 0.76-mm interlayer + 0.76-mm Saflex Clear| 10-mm low iron c#4 with high-reflective, high-transmission, robust solar-control coating)
- Configuration 3: Retail window IGU, low reflection (6-mm low iron, c#1 antireflective coating|0.76-mm interlayer + 0.76-mm Saflex Clear|6-mm low iron [Argon 90% 16 mm], 4-mm low iron c#5 low-e coating)
Figure 1. Schematic depiction of configurations 1-3
(1) 
(2) 
(3)
Note that there may be other considerations regarding the glass that are important for the selection of the final configuration; e.g., if configuration 2 is a clamped construction, there may a need for glass strengthening for reasons other than thermal stress. Or for configuration 3, there might be a requirement to provide burglary resistance to class P4A to EN 356, resulting in an increase in interlayer thickness. Also note that the most effective position of Saflex Solar is typically in front of any solar control coatings or cavities that are present in the configuration to minimize the effect of secondary heat transfer to the inside.
The key performance parameters for the selection of the interlayer are given in Table 1 for the configurations outlined previously for both Saflex Solar SG and Saflex Solar SH, using Saflex Clear as a reference. It is clear that the use of Saflex Solar reduces the visible light transmittance relative to a clear PVB interlayer, with the effect more pronounced for Saflex Solar SG compared to Saflex Solar SH. In contrast, the decrease in g-value is much larger for Saflex Solar SG, providing a significant performance benefit in that respect over Saflex Solar SH in all three configurations.
Key solar performance parameters
Solar direct absorptance always goes up with use of Saflex Solar, but the use of Saflex Solar SG, in many cases, would require the use of strengthened glass; this is not necessarily the case for Saflex Solar SH. In some cases, a strengthening requirement might be an economic or aesthetic barrier for use. In other cases, it is less relevant because the glass would need strengthening anyway due to the stresses occurring under load or the fixation system used. Finally, the color perception through the glass may change slightly with use of Saflex Solar, but CRI values are still above 90 and—particularly for Saflex Solar SH—the difference between Saflex Clear is not very large.
Table 1. Key solar performance parameters as calculated to EN 410
| Interlayer | VLT (%) | g-value | αe,1 (%) | CRI |
| Configuration 1: Basic | ||||
| Saflex Clear | 89 | 0.89 | 16 | 99 |
| Saflex Solar SH | 83 | 0.63 | 41 | 96 |
| Saflex Solar SG | 76 | 0.53 | 55* | 93 |
| Configuration 2: Double-skin façade—outer surface | ||||
| Saflex Clear | 66 | 0.65 | 16 | 98 |
| Saflex Solar SH | 61 | 0.52 | 42 | 99 |
| Saflex Solar SG | 55 | 0.44 | 57* | 95 |
| Configuration 3: Retail window IGU, low reflection | ||||
| Saflex Clear | 83 | 0.58 | 16 | 98 |
| Saflex Solar SH | 78 | 0.47 | 40 | 96 |
| Saflex Solar SG | 71 | 0.38 | 52* | 93 |
Although in the end all of these factors have to be carefully considered by the design engineer with regards to the functional requirements and design intent, having a high-level understanding of the considerations that are important when considering the use of Saflex Solar might be helpful. Many software packages that allow the calculation of optical and solar performance of glazing incorporate Saflex Solar, including but not limited to Optics/Window, WIN SLT, and Glassadvisor.
Saflex Solar is compatible with other Saflex interlayers such as Saflex Clear and Saflex Structural as well as Vanceva® Color Interlayer systems. In specific configurations, Saflex can be advantageously combined with low-e coatings or robust solar control coatings. Plus, Saflex Solar is specifically formulated to provide exceptional durability when exposed to natural weathering.
We hope you can make an informed decision to use either Saflex Solar SG or Saflex Solar SH in your next project now!
