Why Does Glass Break? (2024 Guide on Causes & Prevention)

Table Of Contents

Have you ever wondered why wine glasses shatter into a million pieces as soon as they take an impact?

Or how does that massive glass facade on a skyscraper stay together despite the immense forces constantly acting on it?

Glass has a complex structure — rigid and solid yet fragile at the same time. For something so common, the science behind why glass breaks is complex. This guide explores this complexity in detail and answers the question: Why does glass break?

Why Does Glass Break? (The Molecular Structure of Glass)

The reason glass shatters so easily lies in its molecular structure. Glass is made of silicon dioxide, which forms a rigid, random network of molecules. Unlike most solids—where molecules neatly stack together in a lattice—the silicon and oxygen atoms in glass are connected at random angles in an irregular pattern.

This disordered arrangement gives the glass its transparency and makes it easy to mould into different shapes when heated. However, it also means there are no planes of weakness, so when force is applied, the glass fractures in a jagged, uncontrolled manner. Any tiny surface imperfections or scratches can also act as stress concentrators, initiating cracks that then propagate through the material.

Once a glass crack starts spreading, it’s hard to stop. Although the bonds between the silicon and oxygen atoms are strong, it’s difficult for cracks to change direction or stop at the edge of an imperfection. They just keep going through the random network due to the irregular geometry of the silicon-oxygen bonds.

Glass lacks an ordered structure, so its fractures are difficult to predict. For this same reason, glass is prone to spontaneous breakage without much warning.

The only way to improve impact resistance is by introducing a more orderly molecular arrangement, as in the case of tempered glass. This is achieved by heating and then rapidly cooling the glass, which helps it develop internal compressive stresses. These stresses help counteract crack spread, allowing it to withstand much higher loads before shattering in a relatively safe manner, i.e., into granular chunks and not sharp shards as in regular glass.

Tip: Check out our guide on how to identify tempered glass for more info. Also, if you experience glass breakage in your office building, we recommend hiring experts who offer commercial glass replacement services.

Why Does Glass Break When Heated? (Thermal Stress)

Glass breaks when it experiences thermal stress, i.e., exposure to uneven heat distribution. This temperature imbalance causes the glass to expand unevenly, putting strain on its structure.

When one area of glass heats up, it expands. But the cooler areas don’t expand at the same rate. This imbalance creates internal stresses that pull and warp the glass. If these stresses become too severe, the glass will fracture to relieve the pressure.

The level of thermal stress depends on three factors:

  • The temperature difference between the hot and cold parts of the glass: The greater the difference, the higher the strain.
  • How quickly the temperature changes: Rapid heating or cooling causes the glass to expand or contract faster, increasing stress.
  • The thickness and shape of the glass: Thinner, irregularly shaped glass is more prone to breakage since it’s less able to handle temperature fluctuations.

To minimise thermal stress, avoid exposing glass to extreme or rapid temperature swings. For example, don’t pour boiling water on a cold glass or expose hot glass to freezing temperatures. The shock from such rapid temperature changes can easily cause it to shatter.

Protecting glass from thermal stress is key to preventing cracks and breakage. By controlling temperatures and heating/cooling glass gradually, you can help ensure it remains intact.

Why Does Glass Break With Sound? (Acoustic Fractures)

Have you ever heard a glass suddenly shatter for seemingly no reason? This is known as an acoustic fracture and is caused by sound waves vibrating the glass at its resonant frequency.

When sound waves travel through glass, they cause the glass molecules to vibrate. Each type of glass has a specific frequency range that causes its molecules to vibrate the most, known as its resonant frequency band. If the sound waves match the resonant frequency, the vibrations build up and cause fractures in the glass.

Broken Glass Panel

The fractures typically start as small chips or cracks in the edge or surface of the glass. As the sound waves continue vibrating the glass, these imperfections expand, intersect, and spread through the material. Once the fractures connect and compromise the glass’s structural integrity, the entire sheet shatters.

Acoustic fractures tend to happen more easily in larger panes of glass, as there is more surface area for fractures to form, and the glass’s resonant frequency is lower. They’re also more likely in glazing that’s not properly installed or is damaged, as there are more weak points for fractures to originate from.

To prevent acoustic fractures, choose glass materials with a resonant frequency outside the range of normal environmental noise. Laminated or tempered glass are great options and are more resistant to fracture from sound. Contact professionals for high-level glass installations in a structurally sound frame to reduce the risk of resonant vibrations.

If you frequently hear the specific noise that caused the fracture, it may continue damaging other glass in the area. Identifying and eliminating the sound source is the only way to fully prevent these unpredictable breaks in the future. With the proper precautions taken, glass can remain intact even when exposed to loud noises.

Why Does Glass Break for No Reason? (Spontaneous Breakage)

Despite the absence of an obvious impact or stress, glass spontaneous breakage can occur for these 4 reasons:

  1. Internal Stress: During the glass manufacturing process, uneven cooling can create internal stresses that remain in the glass. Over time, these stresses may cause the glass to weaken and suddenly crack or shatter. This can happen long after the glass has been installed, taking you by surprise. Using glass that has been properly annealed to relieve internal stresses during manufacturing and handling glass with care during installation can help minimise this risk.
  2. Temperature Changes: Why does glass break when hot water is poured in? Rapid or uneven heating and cooling of glass can also introduce stresses that lead to spontaneous breakage. For example, if one area of a glass pane is exposed to direct sunlight while another area remains shaded, the temperature difference can create enough stress to cause the glass to break. Using glass with a low coefficient of expansion—i.e., those less affected by temperature changes—and avoiding extreme or uneven temperature exposures can help prevent this issue.
  3. Edge Damage or Flaws: Nicks, scratches, or microcracks along the edge of a glass pane or subtle flaws within the glass itself act as stress concentrators, making the glass more prone to shattering under temperature changes or pressure. Even small edge damage that goes unnoticed can lead to spontaneous breakage over time. Careful handling and storage of glass to avoid edge damage and purchasing glass from reputable suppliers can reduce the risks of flaws causing unanticipated breakage.
  4. Chemical Reactions: In rare cases, impurities or chemicals within the glass can react to environmental factors like humidity levels or UV exposure and weaken the glass, eventually leading to spontaneous cracking or breakage. Using reputable suppliers that follow industry standards for glass composition and purity is the best way to avoid issues from chemical reactions.

Properly manufactured, handled, and installed glass shouldn’t break spontaneously under normal conditions. However, being aware of these potential contributing factors can help in determining the cause of unpredictable glass breakage — and avoiding it in the future. Ensure you hire glazing experts for your commercial glass installation and repair/refurbishment needs.

5 Tips for Preventing Glass Breakage

Consider these 5 expert tips for strengthening and protecting glass structures in your office building:

  1. Annealing: After the glass is formed, it goes through an annealing process where it’s slowly cooled to room temperature. This relieves internal stresses that could lead to spontaneous breakage. Make sure any glass you purchase has been properly annealed.
  2. Toughening: Toughened or tempered glass goes through a rapid heating and cooling process that makes it much stronger. The glass develops an outer “shell” in compression and an inner section in tension that works concertedly to contain any cracks. For high-risk areas like doors or tables, use toughened glass.

Large Building Interior Communal Seating Area
  1. Laminating: Laminating glass bonds two or more sheets together with a strong interlayer, like polyvinyl butyral (PVB) plastic. This holds the glass together even if broken, preventing dangerous shards from scattering. Laminated glass provides security and safety, ideal for applications like skylights.
  2. Edge Protection: The edges and corners of glass are most susceptible to damage. Installing edge protectors, mouldings, or sealant around the perimeter helps shield the glass from impact. For glass doors or large windows, always use safety glass with polished, rounded edges.
  3. Proper Installation: When installing glass, the framework and any hardware should distribute weight and stress evenly. Make sure the glass is properly secured in a way that prevents excess movement or vibration. For heavy glass panels, multiple points of attachment may be needed to properly support the weight.

Taking proactive measures will save you from dealing with the hassle and cost of frequent glass repairs or replacement. As leading industrial glazing experts in the UK, we offer commercial glass replacement and refurbishment services for your office building glasses. Contact us now to discuss your project details.

Frequently Asked Questions

Why does glass break when dropped? 

Glass breaks when dropped due to its high level of brittleness. Brittle materials have a low elastic limit, which means that they can’t bend or deform to great extents before they break. When a brittle material is subjected to a force, such as the impact of hitting the ground, the force can cause the material to exceed its elastic limit and break.

Why does glass break when frozen?

Glass breaks when frozen because water expands by about 9% in volume when it freezes. If there’s not enough room in the container for the water to expand, it’ll put pressure on the glass and cause it to break.

Even if there’s enough room in the container for the water to expand, the glass may still break if it’s not cooled evenly. This is because glass is a poor conductor of heat, so the outside of the glass may cool down much faster than the inside. This can cause uneven stresses in the glass and cause it to break.

Do inexpensive glasses break more easily?

The price of glassware depends on many factors unrelated to durability, so cost alone doesn’t necessarily indicate how easily it will break. However, higher quality glass is often made of more refined materials and manufactured using higher standards, which can produce glass that’s less prone to breaking. Still, all glass has some level of brittleness and can break if mishandled or exposed to extreme temperatures.


In summary, why does glass break? The answer lies in its brittle nature and irregular molecular structure. Once a crack forms in glass, the entire structure loses stability and collapses. Now that you understand the science behind the shattering of glass, you can take extra precautions to prevent future breakage and choose glass materials and structures wisely based on their intended use. As glazing specialists, we can offer professional advice on which glass type to opt for — contact us today!

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