Glass bottles don’t break in the freezer just because water expands when it freezes. (Bermek/Shutterstock)
In a nutshell
- Glass bottles donât just break because water expands when it freezes. The real culprit is a trapped liquid pocket that gets surrounded by ice and creates extreme pressure when it finally freezes.
- Using smaller bottles (which encourage supercooling and bubble formation) or hydrophobic (water-repellent) coatings can prevent ice from trapping liquid and reduce the risk of breakage.
- The same freezing mechanics that break bottles also contribute to frost damage in roads, buildings, and historical artifacts, making this research relevant beyond kitchen mishaps.
AMSTERDAM â That cracked bottle in your freezer isnât just bad luck; itâs physics plotting against you. Scientists from the University of Amsterdam have finally cracked the case of why glass water bottles shatter when frozen, and itâs not simply expansion. The real culprit? A hidden pocket of liquid that becomes a ticking time bomb as ice forms around it.
âNewton had an apple fall on his head. I found my freezer full of broken glass,â jokes lead author Menno Demmenie from the University of Amsterdam, in a statement.
You probably learned in school that water expands when it freezes, unlike most substances. This expansion is usually blamed when freezing causes damage. But hereâs the thing: if a bottle is only half full, why would it still crack? Shouldnât the ice have room to expand into the empty space? This new research, published in Scientific Reports, takes a closer look at what is happening inside a glass bottle of water as it freezes.
A team of researchers ran over 120 experiments using glass bottles of different sizes. They added blue dye to the water that turns clear when frozen, letting them watch exactly where and when ice forms.
The Trapped Pocket Problem
Menno Demmenie (UvA).)
It turns out the damage doesnât happen simply because water expands when it freezes. It happens because of how ice forms in the container. When water freezes in a bottle, it typically starts freezing from the top, right where the water touches the glass and air. This creates a frozen âlid.â Then the water continues to freeze from the outside in, eventually trapping a pocket of liquid water in the middle, surrounded completely by ice.
When this trapped pocket finally freezes, it has nowhere to expand. The pressure it creates is enormous, enough to dent steel and four times more than a glass bottle can handle. Thatâs why the bottle cracks.
The researchers filmed dozens of samples of blue-dyed water freezing at â30°C (about â22°F). They watched as the ice broke the glass when the top surface froze first, followed by the sides, trapping liquid in the middle.
Surprisingly, it doesnât matter how big or small the trapped pocket is, the pressure it creates is always the same. Thatâs why even bottles with just a little water can still break.
Simple Solutions to Prevent Freezing Damage
Changing the bottleâs surface can completely prevent trapped water pockets. When they treated the glass to make it water-repellent, the water formed a flat surface rather than a curved one. This simple change made the ice start forming from the bottom instead of the top, allowing water to escape upward as freezing continued.
In regular glass containers, water curves up slightly where it meets the glass. Water molecules at this edge donât move around as much, making this spot freeze first.
They also found that smaller containers are less likely to break. Water in smaller bottles cools faster because thereâs more surface area compared to the amount of water. This often causes the water to become âsupercooledââgetting colder than 32°F (0°C) before actually turning to ice.
Supercooled water freezes differently. Instead of forming a solid block, it creates branch-like ice patterns that trap tiny air bubbles. These bubbles act like little shock absorbers, reducing pressure on the container.
This explains why plastic water bottles sometimes survive freezing while glass ones rarely do. According to the researchers, many plastics used in common drink containers have better water-repelling properties than glass, which helps prevent the formation of trapped water pockets during freezing.
Beyond Kitchen Disasters
The same principles explaining the mess in your freeze also apply to frost damage in roads, buildings, and historical monuments. Understanding how ice forms and damages materials could help engineers design better structures for cold climates and help conservators protect valuable artifacts.
When a glass bottle explodes in your freezer, itâs not just water expanding, but a specific sequence of freezing that traps water and creates enormous pressure. If you need to freeze a water bottle, plastic might be the way to go.
Paper Summary
Methodology
The researchers used cylindrical glass vials of different sizes (6.35, 7.35, and 9.35 mm inner radius) and surface treatments (hydrophilic, untreated, and hydrophobic). They added methylene blue dye to water, which remains blue in liquid form but becomes colorless when frozen, allowing clear visualization of the freezing process. Experiments were conducted in a climate chamber at -30°C and recorded with high-speed cameras to capture ice formation dynamics.
Results
Out of 90 untreated glass vials, 59 fractured during freezing. None of the 22 hydrophobic vials broke. In hydrophilic and untreated containers, ice nucleation began at the curved meniscus (water surface), eventually trapping water pockets inside the ice. When these pockets froze, they generated pressures of approximately 260 megapascals, far exceeding the 65 megapascal limit of the glass containers. Containers that experienced âdendriticâ (tree-like) ice formation first were less likely to fracture (53.7%) compared to those with direct crystallization (83.3%), due to trapped air bubbles that acted as pressure buffers.
Limitations
The study focused specifically on cylindrical glass containers at a fixed temperature of -30°C, which is colder than typical household freezers (-18°C). While the underlying mechanisms would remain the same, the rates and patterns of freezing might differ at warmer temperatures. The research also doesnât fully address how these findings apply to different container shapes or to complex microstructures like porous building materials.
Discussion and Takeaways
The findings challenge the common understanding that freezing damage is simply due to waterâs expansion. Instead, they highlight how the formation of trapped liquid pockets is the primary mechanism causing damage. The study offers practical solutions: use water-repellent (hydrophobic) containers and smaller bottles to reduce freezing damage. These insights have implications for infrastructure maintenance, food preservation, art conservation, and cryopreservation of biological samples.
Funding and Disclosures
This research was financially supported by NWO Projectruimte Grant No. 680-91-133. The authors declared no competing interests.
Publication Information
The study, âDamage due to ice crystallization,â was conducted by Menno Demmenie and colleagues from the University of Amsterdam and published in Scientific Reports (2025, Volume 15, Article 2179). It is available under open access terms.
