Reimagining Glass

By Mehmet Arda Ozay, Julian Wang, John C. Mauro 

Glass has been a cornerstone of architecture for centuries, from the windows of cozy homes to the sleek façades of modern skyscrapers. It brings in light, frames our views, and blurs the line between interior and exterior space. While we often admire its clarity, we rarely consider the environmental cost. Behind the transparency lies a surprisingly opaque problem: The global glass industry emits over 86 million tons of carbon dioxide each year, driven largely by the energy-intensive production of soda-lime-silica (SLS) glass, the standard composition used in most architectural glazing. 

SLS glass has remained the dominant glazing material in architectural applications for decades, rooted in production methods established during the Industrial Revolution. Despite significant advancements in structural engineering, building envelope design, and energy performance modeling, the production process and chemical composition of SLS glass have remained essentially the same. This is primarily due to its cost-effectiveness and the established manufacturing infrastructure. However, the high embodied energy and carbon footprint of SLS glass present growing challenges in the context of contemporary sustainability goals. 

SLS production typically involves melting three main raw materials: quartz sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Reaching the required temperatures (around 1450-1500°C) demands a tremendous amount of energy, which accounts for 60-80 percent of the direct carbon footprint. Yet, the environmental impact extends beyond energy consumption. Both soda ash and limestone are carbonates. As they decompose during melting, they release carbon dioxide as a chemical byproduct. This decomposition accounts for 20-40 percent of the overall carbon footprint of the glassmaking process.1, 2 

INTRODUCING LIONGLASS 

In response to the critical environmental challenges posed by conventional glass production, we have pioneered a more sustainable solution. At Penn State, our team has introduced LionGlass™, a novel family of glass compositions offering a fundamentally different and significantly greener approach to architectural glazing. This patent-pending glass family is engineered to dramatically reduce carbon emissions while targeting the rigorous performance standards of modern architectural applications.3 

LionGlass achieves a potential reduction of over 50 percent in the carbon footprint of traditional glass manufacturing through two key innovations: 

1. Lowering the melting temperature by nearly 400°C compared to SLS glass, substantially decreasing energy consumption during production. 

2. Replacing carbonate raw materials with a novel phosphate-based batch, thereby eliminating CO2 emissions caused by carbonate decomposition. 

More than simply an eco-friendly solution, LionGlass offers superior mechanical performance and delivers benefits that extend well beyond carbon accounting for designers and building professionals. Initial testing demonstrates up to a tenfold increase in damage resistance compared to standard SLS glass, resulting in significantly greater durability and safety. This toughness could enable thinner, lighter, and more resilient glazing solutions, which are particularly valuable for advanced applications like triple-pane or vacuum-insulated windows.  

These enhanced mechanical properties could enable LionGlass to better withstand the mechanical and thermal stresses typical in architectural applications. LionGlass also exhibits superior optical clarity compared to SLS glass, as it lacks the greenish tint caused by iron impurities, resulting in clearer, brighter glazing that enhances both visual quality and the effectiveness of daylighting strategies.  

Equally important, LionGlass has been developed to seamlessly integrate with existing architectural systems and workflows. To the naked eye and touch, it performs and appears like any other high-performance architectural glass. Yet at its core, it represents a paradigm shift in how we think about glazing — not as a static material with a fixed environmental footprint, but as a dynamic platform designed to support sustainability goals through lower carbon emissions, improved energy efficiency, and more environmentally responsible manufacturing. 

THE LOW-E CHALLENGE 

While LionGlass aims to redefine strength, clarity, and sustainability in architectural glass, no modern window is truly complete without its essential component: low-emissivity (low-e) coatings. These ultra-thin metallic layers, often just a few nanometers thick, are what give high-performance windows their superpowers  — dramatically reducing unwanted heat gain in the summer and heat loss in the winter. By reflecting infrared radiation while allowing visible light to pass through, low-e coatings help maintain comfortable indoor temperatures, reduce energy consumption for heating and cooling, and improve overall building efficiency. Today, nearly every insulated glazing unit (IGU) on the market relies on these coatings to meet stringent energy codes and performance standards. Their role is so critical that the quality and compatibility of low-e coatings often determine whether a glazing product can truly deliver on its promise of energy savings and occupant comfort. Without this invisible but essential layer, even the most advanced glass would fall short of modern sustainability and performance expectations. That is why one of our key challenges has been to determine if LionGlass can be effectively paired with low-e coatings. 

Low-e coatings are typically engineered specifically for SLS glass, so adapting these sophisticated coatings to a new substrate like LionGlass presents a complex set of challenges. The underlying chemistry of LionGlass differs markedly from SLS, which affects how coatings interact with the surface at a molecular level. Furthermore, variations in surface characteristics, including texture, roughness, and coefficients of thermal expansion, can significantly impact coating adhesion and long-term performance. Since these coatings often consist of delicate silver-based multilayer stacks, they are extremely sensitive to even minor differences in substrate characteristics. Ensuring proper adhesion, preventing delamination, and maintaining thermal compatibility requires careful optimization to achieve the same level of durability and performance that architects and engineers expect from commercial low-e glass products. 

FROM FURNACE TO WINDOW 

To address this challenge, we refined the fabrication process of LionGlass into flat sheets, carefully optimizing every step, from selecting and testing mold materials to fine-tuning post-melting annealing treatments. Achieving a smooth, stable surface was crucial not only to ensure high optical clarity but also to provide the consistent substrate quality necessary for applying delicate thin-film low-e coatings. Controlling surface flatness and minimizing warping were key challenges, as even minor irregularities can impact coating adhesion and overall glazing performance. Through iterative improvements in casting techniques, thermal treatments, and polishing procedures, we established a reliable process to produce the first lab-scale flat sheets of LionGlass that can serve as ideal substrates for applying and evaluating advanced low-e coatings.  

Once the sheets were prepared, we advanced to the coating phase, employing physical vapor deposition (PVD) techniques to apply multilayer low-e stacks. These coatings typically feature silver layers, known for their excellent infrared reflectivity, sandwiched between dielectric materials such as TiO2 or ZnO, which enhance durability, control optical properties, and improve adhesion. This multilayer composition is designed to maximize solar control while maintaining visible transparency, closely replicating the performance of commercial low-e glass. By varying the number and arrangement of silver layers, this approach allows us to optimize the coating structure to meet diverse architectural glazing needs across different climate conditions. 

The preliminary results, primarily based on measurements of optical transmittance and reflectance, have been highly encouraging. Not only did LionGlass accept the applied coatings without adhesion issues, it also demonstrated optical and thermal performance metrics comparable to those of commercially coated SLS glass. As we continue to refine the deposition process and conduct a more comprehensive characterization, we are optimistic that LionGlass will not only match but potentially exceed the performance of conventional SLS-based glazing systems. 

Prototyping the Future 

The next phase of our research focuses on assembling lab-scale prototype insulated glazing units (IGUs) using LionGlass panes, sealed, filled with insulating gases like air or argon, and paired with our optimized low-e coatings. These prototypes will be rigorously evaluated both in laboratory settings and through simulation software to assess their thermal and optical performance. 

Key metrics will include: 

• U-factor, which measures thermal insulation efficiency 
• Visible Light Transmittance (VLT), indicating the amount of natural daylight that passes through 

• Solar Heat Gain Coefficient (SHGC), which captures how well the glazing blocks unwanted solar heat 

By benchmarking LionGlass IGUs against standard SLS-based systems, we aim to determine whether our material can meet or even exceed industry standards while delivering a significantly reduced carbon footprint. 

To ensure long-term viability in diverse climate conditions, these units will also undergo accelerated aging tests, including prolonged exposure to temperature extremes, humidity cycling, and UV radiation. These durability assessments are designed to simulate years of real-world environmental stress, from harsh, freezing winters in Chicago to hot, humid summers in Miami. The goal is not only to prove LionGlass can perform today, but also to ensure it remains reliable for decades to come. 

A MATERIAL DESIGNED FOR THE FUTURE 

What makes LionGlass truly promising goes beyond its novel chemistry to its remarkable adaptability. Rather than requiring an entirely new glazing system with specialized tools or installation methods, LionGlass is designed as a drop-in material that could integrate with existing infrastructure. This opens the door to replacing conventional SLS glass in many applications, from high-performance façades to energy-efficient retrofits. 

Preliminary results suggest that LionGlass may offer several advantages, including: 

• The possibility of using thinner panes without compromising strength 

• Improved optical clarity due to lower impurity levels 

• A reduced likelihood of breakage during transport or installation 

• The potential for significantly lower embodied carbon, beneficial for buildings pursuing LEED certification or net-zero goals 

These benefits remain subject to continued testing and validation as we evaluate LionGlass across a range of performance criteria. 

FROM LAB TO INDUSTRY 

Our vision for LionGlass extends well beyond the lab bench. We are actively engaging with research institutions and companies worldwide to accelerate its journey from scientific discovery to real-world application. One of our most exciting milestones so far is an industrial collaboration with the renowned Italian manufacturer Bormioli Luigi. This partnership led to a successful pilot-scale production trial at their facility in Murano, Italy, where the first pieces of LionGlass drinkware were produced.  

Looking ahead, we are working to scale LionGlass production using industry-standard forming techniques, including the float process, while simultaneously developing coating formulations compatible with commercial manufacturing lines. These efforts are crucial for transitioning LionGlass into architectural glazing applications, where performance, reliability, and process integration are essential. This transformation is fueled by interdisciplinary collaboration, bridging materials science, architectural engineering, and sustainable building innovation to advance LionGlass toward commercial readiness. Our mission is clear: Evolve LionGlass into the next generation of energy-efficient windows, and show how a single lab-scale innovation can reshape the glass industry and contribute meaningfully to a more sustainable built environment. 

We recognize that materials in the built environment shape far more than aesthetics — they determine how buildings perform, endure, and impact the planet. That is why every choice matters. LionGlass challenges the status quo of architectural glazing and invites the industry to reimagine what glass can be. It demonstrates that a material can be both innovative and familiar, high-performing and sustainable, without requiring a complete reinvention of existing systems. The future of glazing does not have to be clear-cut. With LionGlass, it can be clear and smart. 

MEHMET ARDA OZAY is a graduate student in the Departments of Materials Science and Engineering, and Chemical Engineering at Penn State University. 

JULIAN WANG is an Associate Professor in the Department of Architectural Engineering at Penn State University. 

JOHN C. MAURO is the Dorothy Pate Enright Professor and Head of Materials Science and Engineering at Penn State University. 

Citations 

1. Schmitz, A., Kami?ski, J., Maria Scalet, B. & Soria, A. Energy consumption and CO2 emissions of the European glass industry. Energy Policy 39, 142–155 (2011). 

2. Zier, M., Stenzel, P., Kotzur, L. & Stolten, D. A review of decarbonization options for the glass industry. Energy Conversion and Management: X 10, 100083 (2021). 

3. Mauro, J. C. et al. LOW-MELTING GLASS COMPOSITIONS, ARTICLES, AND METHODS OF MAKING THE SAME. WO2023177659A1 (2023). 

CAPTIONS:  

Figure 1: Molten LionGlass being cast into a mold during the initial stages of sample preparation.  

Figure 2: Probability of cracking versus applied force for LionGlass and soda-lime- 
silica (SLS) glass.  

Figure 3: A flat 6x6 inch LionGlass sample produced via controlled casting and annealing. 

Figure 4: Uncoated LionGlass versus LionGlass with low-e coating. 

ALL PHOTOS: PHOTOS: COURTESY OF PENNSYLVANIA STATE UNIVERSITY