Glass is fragile. At least, that is what most people believe. But not all glass breaks easily. Some types can stop bullets. Others can withstand sledgehammer blows. And one material, developed in a Chinese laboratory, is so hard it can scratch the surface of a natural diamond.
This guide compares the strongest glass in the world, from ancient curiosities to cutting-edge materials science. Each entry includes measurable hardness data so you can see exactly how these materials stack up against each other.
What Makes Glass Strong?
Standard window glass is an amorphous solid. Its atoms are arranged in a random, disordered pattern, which is why it cracks easily under stress. Engineers have developed several methods to overcome this weakness.
Tempering heats glass to over 600 degrees Celsius and then cools it rapidly. This process locks the outer surface into compression while the interior remains in tension, making the glass up to five times stronger than untreated glass.
Chemical strengthening replaces smaller sodium ions in the glass surface with larger potassium ions by submerging the glass in a molten salt bath. The larger ions compress the surface, creating a dense, damage-resistant outer layer. This is the process behind Corning’s Gorilla Glass.
Crystalline ordering takes a different approach. Instead of forcing disordered glass to behave better, researchers create materials with small crystalline regions embedded in an amorphous matrix. This hybrid structure combines the transparency of glass with the strength of a crystal. AM-III, the hardest glass-like material ever made, uses exactly this approach.
Measuring Glass Strength: The Key Metrics
Before comparing specific materials, it helps to understand how scientists measure strength and hardness:
- Vickers Hardness (HV): Measures resistance to indentation by pressing a diamond pyramid into the surface under a specific load. Higher values mean harder material. Expressed in gigapascals (GPa).
- Fracture Toughness (KIC): Measures resistance to crack propagation. A higher fracture toughness means the material is less likely to shatter when damaged. Expressed in MPa·m1/2.
- Mohs Hardness: A scratch-based scale from 1 (talc) to 10 (diamond). Useful for quick comparisons but less precise than Vickers.
- Compressive Strength: The maximum load a material can bear before crushing. Relevant for armor and structural applications.
AM-III: The Hardest Glass Material Ever Made
In 2021, researchers at Yanshan University in Hebei, China, announced a breakthrough that redefined what glass can do. Their material, tentatively named AM-III, scored 113 GPa on the Vickers hardness test. Many natural diamonds fall between 50 and 100 GPa on the same scale.
The team created AM-III by compressing fullerene C60 molecules (spherical carbon structures sometimes called “buckyballs”) under 25 GPa of pressure and temperatures of roughly 1,200 degrees Celsius. The resulting material has a density of 3.30 g/cm3, similar to diamond, and contains roughly 94 percent sp3 carbon bonds, the same type that gives diamond its hardness.
What makes AM-III remarkable is its hybrid structure. Unlike conventional glass, which is fully disordered, AM-III contains tiny ordered crystalline regions about 4 angstroms in size embedded within the amorphous matrix. This gives it crystal-like hardness while retaining the ability to be shaped like glass.
Beyond mechanical strength, AM-III is a semiconductor with a bandgap of 1.5 to 2.2 eV, comparable to amorphous silicon used in solar cells. Researchers believe it could eventually be used in photovoltaic panels that require extreme wear resistance, as well as in next-generation bulletproof glass that could be 20 to 100 times tougher than current products.
Compressive strength tests on micrometer-scale pillars showed AM-III can withstand approximately 70 GPa before failure, a figure that approaches diamond’s performance.
Source: Zhang, S. et al., “Discovery of carbon-based strongest and hardest amorphous material,” National Science Review, 2021.
Prince Rupert’s Drops: Strongest Glass You Can Make at Home
Prince Rupert’s Drops are a 17th-century curiosity that still fascinates physicists today. To make one, you drip molten glass into cold water. The glass instantly forms a tadpole shape: a large, round head connected to a thin, elongated tail.
The rapid cooling creates extreme internal stresses. The outer surface solidifies first and compresses inward, while the still-molten interior cools and shrinks later, pulling against the already-rigid shell. The result is a surface compression force of 400 to 700 megapascals, as measured by researchers at the University of Cambridge in 2016.
The head of a Prince Rupert’s Drop can withstand direct hammer blows, hydraulic press compression, and even bullets. High-speed camera footage shows that impacts on the head distribute stress through the entire structure without causing fracture. The tail, however, is the weak point. If you snap or scratch the tail, the entire drop disintegrates explosively into powder in roughly one ten-thousandth of a second.
The name comes from Prince Rupert of the Rhine, who brought samples to the English court in 1660. Scientists did not fully understand the physics until the 20th century, when high-speed photography revealed how crack propagation works inside the drop.
Prince Rupert’s Drops are not a practical building material, but they demonstrate a principle used in modern toughened glass: compressive stress on the surface makes glass dramatically harder to break.
Aluminosilicate Glass: The Strongest Oxide Glass
In 2021, researchers at the University of Bayreuth in Germany created an aluminosilicate glass with a fracture toughness of 1.99 MPa·m1/2, more than double that of Corning’s Gorilla Glass Victus (0.76 MPa·m1/2). Their findings were published in Nature Materials.
The process involved heating aluminosilicate glass to approximately 1,000 degrees Celsius under 15 GPa of pressure, causing partial “paracrystallization.” The resulting material retains some glass-like disorder but gains ordered regions that resist crack propagation.
This glass falls into a narrower category than AM-III. The researchers’ claim applies specifically to “bulk oxide glasses,” meaning glasses made primarily from oxygen-based compounds. Materials like aluminum oxynitride (AlON) and fullerene glass use different chemical compositions and achieve comparable or higher strength.
Aluminum Oxynitride (AlON): Transparent Aluminum Armor
Aluminum oxynitride, marketed as ALON by Surmet Corporation, is a transparent ceramic that looks like glass but performs like armor. It is the hardest polycrystalline transparent ceramic available commercially.
Key mechanical properties of AlON include:
- Knoop hardness: 1,800 kg/mm2 (Mohs hardness ~9, nearly as hard as sapphire)
- Compressive strength: 2.68 GPa
- Fracture toughness: 2.0 MPa·m1/2
- Young’s modulus: 334 GPa
- Thermal stability: Maintains transparency and integrity above 1,100 degrees Celsius
The U.S. Air Force Research Laboratory has tested AlON as a replacement for traditional laminated glass in armored vehicles. Where conventional bulletproof glass might be 3 inches thick, an AlON-based laminate can provide equivalent protection at 1.6 inches or less. This reduces vehicle weight, improves fuel efficiency, and enhances battlefield mobility.
AlON has been shown to stop multiple armor-piercing rounds up to.50 BMG caliber. Beyond military applications, it is used in infrared-optical windows, sensor domes for electro-optical targeting systems, and missile seeker covers where both transparency and extreme durability are required.
Source: Air Force Research Laboratory, 2005; Wikipedia, “Aluminium oxynitride.”
Gorilla Glass, Sapphire Glass, and Commercial Strong Glass
Most consumers encounter strong glass through their smartphones and watches. Two materials dominate this space.
Gorilla Glass, made by Corning, is an alkali-aluminosilicate glass strengthened through an ion exchange process. The latest version, Gorilla Glass Victus, survives drops onto hard surfaces from up to 2 meters and has a fracture toughness of 0.76 MPa·m1/2. Gorilla Glass is currently in its ninth generation and is used in billions of devices worldwide.
Sapphire glass is synthetically grown aluminum oxide (Al2O3), rated at Mohs hardness 9. It is significantly harder than Gorilla Glass and resists scratching from almost anything except diamond. Sapphire glass is used in high-end watch faces, some smartphone camera covers, and select military optical windows. Its drawback is brittleness: while it resists scratches, it can shatter under sharp impact.
Other competitors in the commercial space include Corning’s Dragontrail (used in many Android phones), Schott Xensation, and Tesla Armor Glass, a polymer-layered composite designed for the Cybertruck.
Tempered Glass: The Everyday Strongest Glass
Tempered (toughened) glass is the most widely used safety glass in the world. It is found in car windows, shower doors, glass tables, building facades, and phone screen protectors.
The tempering process heats standard float glass to over 600 degrees Celsius and cools it rapidly with forced air. This creates a surface compression layer that makes tempered glass four to five times stronger than annealed glass of the same thickness.
When tempered glass does break, it fractures into small, relatively harmless pebbles rather than sharp, dangerous shards. This safety property is why building codes in most countries require tempered glass in doors, windows near floors, and skylights.
Comparison: The Strongest Glass Types Ranked
The following table compares the major types of strong glass and glass-like materials by their key mechanical properties.
| Material | Vickers Hardness (GPa) | Fracture Toughness (MPa·m1/2) | Mohs Hardness | Primary Use |
|---|---|---|---|---|
| AM-III | 113 | ~70 (compressive) | ~10+ | Lab/research, future solar cells |
| Natural Diamond | 50–100 | ~5.0 | 10 | Jewelry, cutting tools |
| AlON (Transparent Aluminum) | ~15–20 | 2.0 | ~9 | Military armor, optics |
| Sapphire Glass | ~20 | ~3.0 | 9 | Watch faces, phone cameras |
| Aluminosilicate Glass (Bayreuth) | — | 1.99 | ~6–7 | Research (not yet commercial) |
| Gorilla Glass Victus | ~6–7 | 0.76 | ~6–7 | Smartphones, tablets |
| Tempered Glass | ~5–6 | 0.7–0.8 | ~6 | Windows, car glass, furniture |
| Prince Rupert’s Drop | — | ~0.7 (bulk glass) | ~5.5 | Physics demonstrations |
| Standard Window Glass | ~5 | 0.7 | ~5.5 | Windows, bottles |
Note: Values are approximate and vary by manufacturer, testing method, and specific formulation. AM-III and diamond values come from published research; commercial product values are manufacturer-reported averages.
What Glass Can Withstand Extreme Heat?
Heat resistance is a separate measure from impact strength, but several strong glasses also perform well at high temperatures.
- Borosilicate glass (used in Pyrex laboratory equipment) withstands thermal shock up to approximately 500 degrees Celsius and is resistant to sudden temperature changes.
- Fused quartz glass can handle continuous temperatures above 1,000 degrees Celsius and short exposures up to 1,650 degrees Celsius, making it the standard for high-temperature laboratory and industrial applications.
- AlON maintains full transparency and structural integrity above 1,100 degrees Celsius in air, outperforming most other transparent ceramics.
- Ceramic glass (glass-ceramics like Schott Robax) is used in fireplace doors and wood stove windows, handling sustained temperatures of 700 to 800 degrees Celsius.
For applications requiring both extreme heat resistance and transparency, fused quartz remains the strongest performer. For combined impact and heat resistance, AlON is the leading option. You can learn more about extreme heat-resistant materials in our guide to the most heat-resistant material ever created.
Frequently Asked Questions
What is the strongest glass in the world?
AM-III, a carbon-based amorphous material developed at Yanshan University in China, is the hardest glass-like substance ever measured. It scored 113 GPa on the Vickers hardness test and can scratch natural diamonds. Among commercially available materials, aluminum oxynitride (AlON) is the strongest transparent ceramic.
Which glass is the hardest to break?
For practical, everyday use, laminated glass and tempered glass are the hardest to break. Laminated glass holds together even when cracked due to its plastic interlayer. For extreme applications, AlON transparent armor can stop armor-piercing.50 caliber rounds.
Why are Prince Rupert’s Drops so strong?
Rapid cooling creates extreme internal stresses. The outer shell compresses inward with forces of 400 to 700 megapascals, while the interior remains in tension. This compressive surface layer makes the head nearly impossible to break. However, disturbing the thin tail releases all stored energy at once, causing the entire drop to explode.
Can glass be harder than diamond?
Yes. AM-III, developed in 2021, scores higher on the Vickers hardness test (113 GPa) than most natural diamonds (50 to 100 GPa). However, AM-III is a carbon-based material rather than a traditional silicate glass, and it is not yet commercially available.
What is the strongest phone screen glass?
Corning Gorilla Glass Victus is the most widely used high-strength phone screen glass, surviving 2-meter drops onto rough surfaces. Sapphire glass is harder and more scratch-resistant but more brittle. Some manufacturers use both: sapphire for camera covers and Gorilla Glass for the main display.
Is bulletproof glass really glass?
Traditional bulletproof glass is laminated alternating layers of glass and polycarbonate plastic. Advanced versions use AlON ceramic as the strike face. Pure glass alone cannot stop bullets, but the layered composite structure absorbs and distributes impact energy across multiple layers.
The Future of Strong Glass
Materials science is pushing the boundaries of what glass can do. The strongest glass in the world today, AM-III, exists only in laboratory quantities, but its unique combination of hardness, transparency, and semiconducting properties suggests a future where glass-based materials replace traditional armor, enable more durable solar panels, and protect devices in ways current materials cannot.
AlON is already deployed in military applications and is gradually moving into civilian security and aerospace markets. Meanwhile, consumer glass continues to improve: each generation of Gorilla Glass and its competitors brings incremental gains in drop resistance and scratch hardness.
The gap between laboratory breakthroughs and commercial products is closing. Within the next decade, materials inspired by AM-III’s hybrid crystal-glass structure could make the strongest glass in the world not just a scientific curiosity but an everyday reality.
