Saint-Gobain's COOL-LITE Xtreme 51/23 Pushes Solar Control Selectivity to 2.22—And Adds a Low-Carbon Substrate Option

A New Benchmark in Triple-Silver Solar Control

Saint-Gobain Glass has rolled out the latest addition to its Cool-Lite Xtreme solar control range, and the performance numbers are aggressive enough to warrant a fresh look from façade designers working in cooling-dominated climates and highly glazed buildings.

Cool-Lite Xtreme 51/23 (annealed) and 51/23 II (to-be-tempered) provide the highest selectivity in the Xtreme portfolio, combining a light transmission of 51% with a remarkably low solar factor of just 23%. This results in a selectivity of 2.22, allowing more natural daylight to enter while effectively managing solar heat gain — a critical balance for creating liveable, comfortable spaces, even in highly glazed buildings.

For context, selectivity (the ratio of visible light transmission to solar heat gain coefficient) is the single most useful metric for evaluating solar control coatings on view glass. A selectivity above 2.0 is considered high performance; 2.22 places this product near the top of what triple-silver low-e chemistry can currently deliver in a commercially available coated lite.

What's Changed for Specifiers

The launch isn't just a performance bump — it changes how the product can be specified and processed:

• Annealed option, finally. The launch introduces the first annealed version of this specification to the Xtreme range, giving fabricators, architects and specifiers greater design flexibility. Both versions deliver identical performance and visual qualities, regardless of whether the glass is tempered or not. Until now, the highest-selectivity Xtreme products were tempered-only, which limited their use in projects where heat-treatment wasn't required.
• Cleaner processing. The to-be-tempered Cool-Lite Xtreme 51/23 II version also comes with EasyPro surface protection, making handling and processing simpler, cleaner — a small but meaningful detail for IGU fabricators dealing with soft-coat handling losses.
• Replaces 50/22 II. This new product will replace the outgoing Cool-Lite Xtreme 50/22 II, offering improved aesthetics and, for the first time in this performance category, an annealed version to complement the to-be-tempered option. It joins the existing Cool-Lite Xtreme family, including 70/33 (II) and 61/29 (II), and will be manufactured in Saint-Gobain's high-tech facility in Germany.

The Low-Carbon Story That Actually Matters

The more strategic announcement — and one that should be on the radar of anyone writing performance specs for projects with embodied carbon limits — is the substrate flexibility. Cool-Lite Xtreme 51/23 (II) is available on Planiclear standard float glass, Diamant low-iron glass, and Oraé low-carbon glass. Saint-Gobain says the availability on Oraé makes it possible to specify a high-performance solar control solution while reducing both operational and embodied carbon, helping projects meet increasingly stringent environmental targets without compromise.

Oraé is Saint-Gobain's reduced-carbon flat glass, produced using high cullet content and renewable energy. The ability to combine a top-tier solar control coating with a low-carbon substrate is significant because, historically, sustainability-minded teams have had to choose: either spec the best-performing coating (often only available on standard float) or accept a performance compromise to get the embodied-carbon reduction. That trade-off is starting to disappear.

Practical Implications

For architects and envelope consultants working under codes such as the 2024 IECC, ASHRAE 90.1-2022, NYC LL97, and Title 24, the implications stack up quickly:

• Cooling load reduction. A 23% solar factor pushes solar heat gain coefficients well below most prescriptive code thresholds for southern climates and high WWR projects, potentially shrinking mechanical equipment sizing and recurring energy spend.
• Daylighting credit retention. Holding 51% visible light transmission preserves access to daylighting credits in LEED v4.1/v5 and WELL, which often get sacrificed when designers chase low SHGC numbers.
• Embodied carbon accounting. Pairing the coating with Oraé gives spec writers a defensible line item in an EPD-driven submittal package, particularly for projects pursuing LEED v5, the GSA's new federal procurement targets, or local embodied-carbon caps.
• Procurement risk. German manufacturing means North American specifiers need to plan lead times and verify distribution agreements with their preferred IGU fabricators before locking the product into a tight construction schedule.

The broader takeaway: as competing coaters chase the same selectivity ceiling, the differentiator increasingly isn't the coating performance itself but the substrate options behind it. Expect more product families to follow this same playbook over the next 18 months.