What Glass Brick Is
Glass brick, also called glass block, is a building material made entirely of glass. You can find it in various sizes, shapes, textures, and colors. It lets light pass through while obscuring visibility. This makes it useful when you want privacy without sacrificing illumination. Modern glass blocks came from early 20th century prism lighting, invented to brighten industrial spaces. They offer insulation, brightness, and privacy all at once.
Early Developments in the 19th Century (1850s–1890s)
Sidewalk vault lights were an important step toward today's hollow glass bricks. These ground-level prisms reflected daylight into dim cellar and basement areas. Then in the 1880s, Swiss architect Gustave Falconnier invented the first hollow glass block in France. His bricks were blown glass molded into hollow shapes and joined by wire and cement. Available in multiple colors, they were pitched for greenhouse roofs and walls. That design offered thermal insulation because glass does not conduct heat well. It also sealed moisture out and resisted dust and tarnish.
Early 20th Century Growth
By 1914, glass brick had entered mainstream architecture with Bruno Taut’s Glass Pavilion, one of the era’s signature glass buildings. The 1930s saw even more use of glass blocks, especially in Art Deco and Streamline Moderne styles. Architects built walls of these bricks to let daylight in and to glow softly from inside at night.
Mid and Late 20th Century Use
Glass blocks remained popular through the 20th century. In the 1970s, the Japanese architect Tadao Ando used them for courtyard walls in homes across Osaka. These installations balanced light, aesthetic, and architectural discipline.
Current Use in the 21st Century
Glass bricks are less widespread in mainstream modern architecture today. Yet they remain favored in bathrooms and washrooms. They diffuse daylight nicely while maintaining privacy through their diffraction properties. They also appear in art pieces, such as Chicago’s Crown Fountain, which features two illuminated glass block towers.
How Glass Blocks Look and What They’re Made For
Appearance
Glass blocks come in all kinds of finishes. The surface can be smooth or textured, depending on how the glass cools and what gets pressed into it during production. Some patterns are molded into the outer surface, while others are formed inside the hollow part. The goal is to change how much light comes through or to distort what’s seen behind it. That’s what makes them useful for privacy or design. Color can vary too, and extra touches like glazes or decorative inserts are sometimes added to get a specific look or level of privacy.
Standards and Grading
Glass blocks are made according to specific rules. In Europe, they follow the EN1052-2 standard. Internationally, it’s ISO TC 160/SG1. These standards allow for some size differences and small imperfections during production. Blocks fall into three quality classes. Class 1 is the best, allowing only a 1-millimeter difference from the intended size or shape. Class 2 and Class 3 have looser standards.
Insulation Value
Glass bricks offer decent insulation. Their R-value ranges from 1.75 to 1.96, which is close to what you get with regular double-pane windows. Some newer versions go further. They’re made with argon gas sealed inside and a low-emissivity glass layer in between. That brings the U-value to about 1.5 W per square meter per Kelvin. For context, triple-pane windows usually sit at 1.8, and high-end double-pane windows with advanced coatings can hit 1.2. So, glass blocks with these upgrades fall somewhere in the middle.
How They’re Used
Wall Blocks
Glass blocks are often used in walls where light and looks matter more than structure. Standard hollow glass wall blocks don’t hold weight unless they’re specifically designed for that. They're made by pressing two halves of molten glass together, then cooling them down slowly. The center stays hollow, forming a partial vacuum, which helps with insulation but lowers the strength. These blocks don’t work like normal bricks in terms of load-bearing. They’re used in curtain walls and set inside frames. When framed with steel or masonry, you can build a glass block wall up to 144 square feet. Without a frame, the limit drops to 100 square feet.
One of the first buildings to feature glass block walls was the William Lescaze House and Office in New York City, built in 1934. It was the first residential building in the city to use them for walls.
Skylights and Sidewalk Lighting
Glass blocks used for floors or sidewalks are built differently. These are either solid or have much thicker walls than the ones used in vertical walls. They’re set into metal frames or poured into reinforced concrete grids. That way, they can safely span openings like basement ceilings or rooftop gaps and serve as skylights. Regular wall blocks can’t handle that kind of load, so they shouldn’t be used in floors.
How They’re Built
There are a few ways to put glass wall blocks together. The most common method is laying them with Portland cement mortar and placing steel reinforcing rods between rows for added strength. The design and reinforcement layout usually follow what the architect or block manufacturer recommends.
Some builders use different systems that don’t require mortar. These use timber or PVC frames to hold the blocks in place. These systems are often quicker to install and are used in some commercial or prefab applications.
Specialty Glass Bricks and Their Uses
Glass bricks come in more than just the standard kind. There are special types made for specific jobs. These versions focus on things like safety, insulation, fire protection, or color. The way they’re built changes based on what they need to do.
Bulletproof and Vandal-Resistant Bricks
For high-security areas, some glass blocks are built to stand up to impact. These are either made from solid glass or have extra-thick walls. They’re a lot like the tough glass used in sidewalks and pavement lights. The thick design helps them hold up against bullets and physical attacks.
Fire-Resistant Glass Blocks
Regular hollow glass bricks don’t do much against fire. But there are versions designed to hold up better in extreme heat. Some have thicker outer walls to slow down heat transfer. Others include a fire-resistant layer added between the two glass halves during production. Some makers bond two bricks together using a special adhesive to create extra-thick blocks, sometimes as thick as 160 millimeters. That added depth boosts fire resistance even more. Still, these fire-rated bricks need to be installed the right way. If not, the wall won’t actually meet fire safety standards. Following the manufacturer’s guidelines during setup is essential.
Gas-Insulated Glass Blocks
Another upgrade involves adding argon gas inside the hollow part of the brick. This kind of gas-insulated glass block keeps heat from passing through easily. It gives much better thermal insulation than regular hollow bricks. It’s a newer method and helps improve energy efficiency in buildings.
Colored Glass Bricks
Some glass bricks come in colors. There are two ways to get the color in. One method uses UV-stable colored glass, which can go anywhere regular bricks go. The color is built into the glass and holds up in sunlight. The second method adds a dye or clear paint into the hollow center. This creates bolder, brighter shades not possible with colored glass alone. But there’s a catch. These painted colors may fade if exposed to strong sunlight over time, so they’re not ideal for outdoor or sun-facing areas.
