Curtain walls, as the iconic exterior enclosure of modern high-rise buildings, rely heavily on glass materials that balance aesthetics, safety, energy efficiency, and structural performance. The selection of curtain wall glass is tailored to project requirements such as building height, climate conditions, functional needs, and budget constraints. Below is a detailed breakdown of the main glass types used in curtain walls, their characteristics, and application scenarios.
1. Tempered Glass and Heat-Strengthened Glass
1.1 Tempered Glass
Tempered glass is produced by heating float glass to approximately 620℃ until slightly softened and then rapidly cooling its surface with cold air. This process creates compressive stress on the surface and tensile stress inside, enhancing its strength by 3-5 times compared to ordinary glass. A key safety feature is that it shatters into small, blunt-edged fragments, minimizing injury risks.
However, tempered glass has an inherent risk of spontaneous explosion, primarily caused by phase transformation and volume expansion of nickel sulfide (NiS) impurities within the glass. While heat soak testing (HST) can reduce this risk by heating the glass to around 290℃ to induce premature explosion of defective pieces in the factory, it increases costs by 1-4 times and cannot completely eliminate the issue. It is commonly used in low-rise curtain walls, doorways, and glass railings below 5 meters in height.
1.2 Heat-Strengthened Glass
Heat-strengthened glass undergoes a similar heat treatment process to tempered glass but with gentler cooling, resulting in a surface stress range of 24-69MPa (lower than tempered glass’s ≥95MPa). It has no risk of spontaneous explosion, and when broken, forms large, interlocking fragments that remain attached to the frame due to structural adhesive, maintaining residual strength and allowing time for maintenance.
With better flatness and appearance after coating compared to tempered glass, it is preferred in high-rise curtain walls overseas and in Hong Kong, such as the Jin Mao Tower in Shanghai and Two International Finance Centre in Hong Kong. It is often combined with laminated and insulated glass for enhanced performance.
2. Laminated Glass
Laminated glass consists of two or more glass sheets bonded with interlayers such as PVB (Polyvinyl Butyral) or EVA (Ethylene Vinyl Acetate) films through high temperature and pressure. The interlayer acts as a cohesive layer—even if the glass breaks, fragments adhere to the film, preventing falling and ensuring safety.
It offers excellent impact resistance, sound insulation (sound transmission loss up to 35-45dB when combined with insulated glass), and UV protection (blocking over 99% of UV rays in high-end products). With no spontaneous explosion risk and a service life of over 25 years for high-quality films, it is ideal for super high-rise buildings, crowded public areas (airports, shopping malls), and coastal typhoon-prone regions. For example, the new headquarters of the Independent Commission Against Corruption in Hong Kong uses heat-strengthened laminated insulated glass for its main curtain wall.
3. Insulated Glass
Insulated glass (also known as double-glazed or triple-glazed glass) comprises two or more glass panes separated by a spacer and hermetically sealed to form a dry gas cavity (air or inert gas such as argon). This structure significantly reduces heat transfer, with a U-value of 2.5-3.2W/(m²·K) for standard insulated glass, far lower than the 5.2-6.0W/(m²·K) of single-pane glass.
Filling the cavity with argon further reduces the U-value by 0.2-0.3W/(m²·K) and improves sound insulation. The spacer, often aluminum filled with desiccant, maintains cavity dryness and prevents condensation. It is widely used in curtain walls to meet basic energy-saving and sound-insulation needs, with configurations like 5+12A+5 (5mm glass + 12mm air gap + 5mm glass) being common. Triple-glazed insulated glass (e.g., 5+9A+5+9A+5) is preferred in cold regions for enhanced thermal insulation.
4. High-Performance Coated Glass
4.1 Low-E Glass
Low-E (Low-Emissivity) glass features a thin metal coating (usually containing silver layers) that selectively reflects far-infrared radiation while maintaining high visible light transmittance (up to 95%). It achieves bidirectional energy savings—retaining indoor heat in winter and blocking outdoor heat in summer. Single-silver Low-E insulated glass has a U-value of 1.5-2.1W/(m²·K), while double-silver and triple-silver variants offer superior shading coefficients (0.30-0.60) and insulation, making them suitable for energy-efficient buildings in hot-summer and cold-winter regions.
It is a staple in landmark buildings like the Shanghai Tower and Burj Khalifa in Dubai, but its cost is 5 times that of ordinary glass, with double-silver/triple-silver products priced at 800-1500 yuan/㎡.
4.2 Solar Control Coated Glass
Also known as heat-reflective glass, it has a metal or metal oxide coating that reflects 30%-40% of solar radiation (vs. 7%-8% for ordinary glass). It provides shading, reduces glare, and creates a mirrored aesthetic with colors like gold, bronze, gray, and blue. However, it may cause light pollution and increase heating loads in winter, so it is often used in office buildings and privacy-sensitive areas (banks, government buildings).
5. Composite Glass Systems
Modern curtain walls typically use composite glass systems to integrate multiple functions:
• Low-E Insulated Glass: Combines energy efficiency and thermal insulation, meeting energy-saving standards for public buildings in most regions.
• Laminated Insulated Glass: Integrates safety (anti-fall), sound insulation, and thermal insulation, ideal for high-rise and noisy environments (airport vicinity).
• Heat-Strengthened Laminated Insulated Glass: Balances safety (no spontaneous explosion), structural stability, and energy efficiency, widely used in high-end commercial and residential curtain walls.
Selection Principles
Curtain wall glass selection should prioritize human-centric design and comply with standards such as GB17841-1999 and GB/T21086-2007. Key considerations include:
1. Safety: Use tempered glass for low-rise areas and laminated/heat-strengthened laminated glass for high-rises and crowded spaces.
2. Energy Efficiency: Adopt Low-E insulated glass in hot-summer and cold-winter regions; triple-glazed systems in extremely cold areas.
3. Sound Insulation: Choose laminated insulated glass for areas with high noise (roads, airports).
4. Cost: Tempered glass offers cost advantages for budget-limited projects, while laminated glass provides better lifecycle value for high-end projects.
In summary, curtain wall glass has evolved from single-pane products to multi-functional composite systems, with safety, energy efficiency, and aesthetics remaining core drivers of innovation and selection.
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