What If? Lab
What if glass were bendy?
Glass is hard. If you drop a glass, it can break! What if glass were bendy instead? Let's imagine it with Olly.
Glass is made by melting sand and cooling it quickly. When it's cool, it's hard and brittle, so it cracks instead of bending. But hot glass is soft, and glass thinner than paper can bend. Imagine glass that was bendy and follow what might change.
Glass is an amorphous solid: hard, brittle and transparent when cool, viscous when hot. Engineers already tame its brittleness with tempering and lamination and make glass thin enough to fold. This thought experiment imagines bendy glass and explores safety, shaping and folding screens.
The big question
Look around. Windows, jars and screens are made of glass.
Glass is hard and you can see through it. But it can crack. What if it could bend?
Glass is everywhere: windows, jars, light bulbs, eyeglasses and the screen you might be reading this on. It lets light through, it is hard, and it stands up to rain and weather. But knock a glass off the table and it may shatter, because glass doesn't bend before it breaks.
So what if glass were bendy? This lab is a thought experiment. Real glass already surprises us: when it's hot it is soft, and when it's thin enough it can flex.
Britannica describes glass as an inorganic solid that is usually transparent or translucent, hard, brittle and impervious to the natural elements, used in everything from buildings to telecommunications. Most types are easily fractured by a blow or shock.
This thought experiment asks what would change if glass were flexible, and uses the question to explore why ordinary glass is brittle, how hot glass is shaped, and how engineers make glass that bends.
Explore the idea
Make a prediction
What happens to glass when it gets very hot?
What happens to glass when it is heated until it glows?
How does glass behave above its working temperature?
- It turns soft and can be shaped
- It turns back into sand
- It gets even harder
-
Established fact
Cool glass is hard and can crack.
Cool glass is hard and brittle; most kinds break easily from a blow or a shock.
Glass is rigid and brittle at room temperature and fails by fracture (Britannica).
-
Established fact
Hot glass is soft, and very thin glass can bend.
Glass passes through a gooey stage as it cools, and glass thinner than paper can flex.
Glass is viscous while cooling, and ultra-thin, ion-exchanged glass can bend repeatedly (Britannica; MIT Technology Review).
-
An idea scientists discuss
Bendy glass is pretend. We imagine it carefully.
What a world of bendy glass would be like is an idea, worked out from how glass behaves today.
All consequences of a flexible bulk glass are reasoned, not observed.
-
Established fact
Glass is hard, and it can break if it is hit.
Glass is hard and brittle, and most kinds break easily from a blow or a shock.
Glass is usually transparent, hard and brittle; most types are easily fractured by a blow or shock (Britannica).
-
An idea scientists discuss
Bendy glass might bounce instead of breaking.
If glass could bend, dropped glasses and jars might survive more often.
Flexible glass might reduce breakage; whether it could stay clear and flat is a separate question this lab explores.
-
Established fact
Some safety glass has plastic in the middle.
Laminated safety glass has a thin layer of plastic between two sheets of glass, so when it's hit it bulges or breaks into small pieces.
Laminated safety glass bonds two sheets around a thin plastic interlayer; when struck it bulges or breaks into tiny, relatively harmless fragments (Britannica).
-
Established fact
Heating and cooling glass fast makes it stronger.
Tempered glass is heated to about 650 °C and chilled suddenly. That makes it about six times stronger.
Tempering at about 650 °C followed by sudden chilling increases strength approximately sixfold (Britannica).
-
An idea scientists discuss
Bendy windows might wobble in the wind.
Bendy windows might be safer, but they might also sag or wobble and make the world look wavy through them.
Stiffness keeps glazing flat and optically true; a compliant glass might trade breakage for distortion. This is reasoning, not data.
-
Established fact
Hot glass is soft and can be blown into shapes.
Glassblowing was probably invented in the 1st century BCE by glassmakers in Syria. Glass can be blown into a mold or shaped freely.
Glassblowing was probably developed during the 1st century BCE by Syrian glassmakers; glass could be blown into a mold or shaped free-form (Britannica).
-
Established fact
Window glass is made flat on melted metal.
Most window glass is made by floating melted glass on a pool of melted tin to give it a flat surface.
Most window glass is made by floating molten glass on molten tin to produce a flat surface (Royal Society of Chemistry, Tin).
-
An idea scientists discuss
Bendy glass might keep changing shape.
If glass stayed bendy after cooling, a vase or bottle might not keep its shape for long.
Rigidity at room temperature is what preserves a formed shape; a permanently compliant glass might creep. A reasoned idea only.
-
Established fact
Some glass is thinner than a sheet of paper.
Paper is about 100 micrometers thick. In 2016, Schott showed flexible glass sheets just 70 micrometers thick and said it could make glass as thin as 20 micrometers.
A sheet of office paper is about 100 micrometers thick; Schott's flexible sheets of 70 micrometers bend, and in 2016 the company made glass as thin as 20 micrometers (MIT Technology Review, 2016).
-
Established fact
Folding phones can use very thin glass.
Schott says its ultra-thin glass for folding phones can bend more than 300,000 times, around a curve with a radius of less than 1 millimeter.
Schott states that its UTG reaches a bending radius below 1 millimeter after processing, needs chemical strengthening, and can bend more than 300,000 times (company claims).
-
An idea scientists discuss
Maybe one day windows could roll up!
If all glass were bendy, screens, windows and bottles might fold or roll, but thin glass is still glass and can break.
Ultra-thin glass hints at what flexible glass might enable; extending it to bulk glass is speculation, since thin sheets bend only because they are thin.
How glass is made
Glass is made from sand. The sand is melted in a very hot oven.
Then it cools down fast. It becomes hard, clear glass.
Most glass is made from three main ingredients: sand, limestone and a chemical called soda (sodium carbonate). They are heated until they melt into a glowing liquid, then cooled quickly. Cooling it fast stops visible crystals from forming.
Sand on its own melts at more than 1,700 degrees Celsius. Adding soda lowers that temperature a lot, and limestone keeps the glass from dissolving in water. As glass cools, it passes through a thick, gooey stage before it turns hard.
Glass is made by cooling molten ingredients such as silica sand quickly enough to prevent visible crystals forming. Most commercial glass is soda-lime-silica: sand (SiO₂), limestone (CaCO₃) and sodium carbonate. Crystalline silica melts above 1,700 °C; adding about 25 percent sodium oxide as a flux lowers this to 850 °C, but the result dissolves in water, so lime is added to make it insoluble again.
The optimum composition is about 75 percent silica, 10 percent lime and 15 percent soda. All glasses pass through a viscous stage as they cool from a fluid state.
Make glass bendy
Pretend glass could bend like rubber. A dropped glass might just bounce!
But a bendy window might wobble in the wind. Would you like that?
Imagine glass that bent instead of cracking. A dropped jar might bounce, and a ball might make a window bulge instead of breaking it. That could make glass much safer.
But bendiness might cause problems too. A floppy window might sag or wobble, and a bendy lens in your glasses might not keep its shape. These are ideas. In the real world, engineers already make some glass safer and some glass bendy in clever ways.
Flexible glass might reduce injuries from breakage and make lighter, tougher containers. But the same stiffness that makes glass brittle also keeps windows flat and lenses precisely shaped, so a uniformly bendy glass might be worse for optics and structures.
These consequences are reasoned speculation. The real world offers partial versions: laminated glass bulges when struck, tempered glass is about six times stronger, and ultra-thin glass flexes because it is thin, not because the material has changed.
Why glass is brittle
Cool glass is very stiff. It cannot stretch, so it cracks.
Hot glass is soft and gooey. Glassmakers shape it while it's hot.
When glass is cool, it is rigid: it can't stretch or bend much. Push it too hard and a crack races through it instead. That's what brittle means.
Heat changes everything. Hot glass is soft and gooey, so people can shape it. Glassblowing was probably invented about 2,000 years ago by glassmakers in Syria. And most window glass is made flat by floating melted glass on a pool of melted tin.
Cooled below its viscous range, glass is rigid and fails by brittle fracture, typically with a conchoidal (shell-like) break. A sudden temperature change also sets up stresses that can crack it; borosilicate cookware glass resists this because its thermal expansion is only a third that of soda-lime glass.
Above that range, glass is workable. Glassblowing was probably developed in the 1st century BCE by glassmakers in Syria, allowing free-form or mold-blown shapes. Today most window glass is made flat by floating molten glass on molten tin (Royal Society of Chemistry).
Safer glass and bendy glass
Car windows use safety glass. Some has a thin layer of plastic in the middle.
Very, very thin glass can bend. Some phones that fold use it!
Safety glass is made in two ways. One sandwiches a thin sheet of plastic between two sheets of glass, so the glass bulges and holds together when hit. The other heats glass to about 650 °C and then chills it suddenly, which makes it about six times stronger. When it does break, it crumbles into blunt little pieces.
Glassmakers can also make glass thinner than a sheet of paper. Glass that thin can bend. One glassmaker, Schott, says its ultra-thin glass for folding phones can bend more than 300,000 times.
Safety glass either laminates two sheets around a plastic interlayer (Édouard Bénédictus patented the idea in 1909; polyvinyl butyral became standard after 1936) or is tempered at about 650 °C and suddenly chilled, raising strength about sixfold so that it breaks into blunt granules.
Flexibility comes from thinness. In 2016 Schott reported making glass as thin as 20 micrometers, strengthened by ion exchange in a bath of molten potassium, where larger potassium ions replace smaller sodium ions and create compression within the glass. Schott says its ultra-thin glass for foldable devices reaches a bending radius below 1 millimeter after processing and can bend more than 300,000 times.
Amazing facts
-
Window glass floats on melted metal while it is made.
Most window glass is made flat by floating melted glass on a pool of melted tin.
Float glass gets its flat surface from molten tin, one of tin's major uses (Royal Society of Chemistry).
-
Soda helps sand melt.
Sand alone melts above 1,700 °C. Adding soda lowers that to about 850 °C, but then the glass would dissolve in water, so limestone is added too.
About 25 percent sodium oxide lowers silica's melting point from 1,723 to 850 °C; lime restores insolubility (Britannica).
-
Glassmakers carry rolls of glass!
In 2016, Schott showed off flexible glass in a roll half a meter wide and half a kilometer long, like a fat roll of cellophane.
In 2016 Schott said it could manufacture ultrathin glass continuously in sheets kilometers long; a demonstration spool was half a meter wide and half a kilometer long (MIT Technology Review).
-
Some glass carries light signals.
Super-clear glass fibers carry messages as pulses of light in fiber-optic cables.
High-purity, ultratransparent oxide glasses carry light pulses in fiber-optic telecommunications (Britannica).
Words to know
- brittle
- hard but likely to crack or shatter instead of bending
- silica
- the main substance in sand, silicon dioxide, used to make glass
- tempered glass
- glass heated and then cooled very fast so it is stronger and breaks into blunt pieces
- laminated glass
- safety glass made of two glass sheets with a thin plastic layer between them
- micrometer
- one thousandth of a millimeter
- flexible
- able to bend without breaking
Discovery challenge
-
What is glass mostly made from?
What is the main ingredient of most glass?
What is the principal raw material of soda-lime-silica glass?
- Sand
- Salt
- Wood
Show the answer
Sand
Sand!
Sand, with limestone and soda.
Silica sand, about 75 percent of the optimum composition.
-
What happens to very hot glass?
What happens to glass when it is very hot?
How does glass behave in its working temperature range?
- It turns soft and can be shaped
- It turns to dust
- It gets harder
Show the answer
It turns soft and can be shaped
It gets soft and gooey.
It gets soft and gooey, so it can be blown and shaped.
It is viscous, which allows blowing, pressing and drawing.
-
Why can very thin glass bend?
Why can ultra-thin glass bend when a window can't?
What mainly makes ultra-thin glass flexible?
- Because it is so thin
- Because it is made of plastic
- Because it is always warm
Show the answer
Because it is so thin
Because it is so thin.
Thinner glass is more flexible, as long as it's strengthened.
Its thinness; ion exchange strengthens it to survive bending.
-
What is in the middle of some safety glass?
What is sandwiched inside laminated safety glass?
What forms the interlayer of laminated glass?
- A thin layer of plastic
- A layer of water
- A sheet of paper
Show the answer
A thin layer of plastic
A thin layer of plastic.
A thin layer of plastic that holds the glass together.
A plastic interlayer, polyvinyl butyral since 1936.
Experiments to try
- Watch What If? Lab What if cakes had no baking powder? Look closely at a slice of cake and you'll see it is full of tiny holes. Baking powder makes bubbles of a gas called carbon dioxide, and those bubbles puff up the batter as it bakes. Imagine baking with no baking powder and follow what might happen.
- Watch What If? Lab What if metal never rusted? Rust forms when iron and steel react with oxygen and water. It slowly eats away bikes, gates and even giant bridges, so people fight it with paint, zinc and special steels. Imagine a world where metal never rusted and follow what might change.
Explore next
- Watch What If? Lab What if cakes had no baking powder? Look closely at a slice of cake and you'll see it is full of tiny holes. Baking powder makes bubbles of a gas called carbon dioxide, and those bubbles puff up the batter as it bakes. Imagine baking with no baking powder and follow what might happen.
- Watch What If? Lab What if metal never rusted? Rust forms when iron and steel react with oxygen and water. It slowly eats away bikes, gates and even giant bridges, so people fight it with paint, zinc and special steels. Imagine a world where metal never rusted and follow what might change.
-
Watch
Landmark
Louvre Museum
The Louvre in Paris began as a castle in 1190, grew into a royal palace and became a museum in 1793. About 30,000 works of art are on show, including the Mona Lisa. Since 1989, visitors have entered through a glass pyramid; 9 million came in 2025.
- Watch Try it What If? Lab What if a balloon floated very high? As a balloon floats higher, the air around it gets thinner and pushes on it less, so the gas inside spreads out and the balloon swells. In our model, a perfectly stretchy balloon launched at sea level is about 14 times its starting size by the time it reaches 20 kilometers.
- Watch What If? Lab What if apples never turned brown? When an apple is cut, a natural chemical in it mixes with oxygen from the air, and the fruit turns brown. Lemon juice and the fridge slow it down, and some apples are now grown to brown less. Imagine apples that never browned and follow what might change.
- Watch What If? Lab What if bubbles could last forever? A soap bubble's skin is a thin sandwich of soap and water, and it pops when the water drains or dries away. Scientists in France made a bubble that lasted 465 days. Imagine bubbles that lasted forever and follow the clues: thin films, drying out and frozen bubbles.
- Watch What If? Lab What if colors never faded? Leave a bright poster in a sunny window and, over weeks, its colors grow pale. Light slowly changes the colored molecules in dyes and inks. Imagine a world where colors never faded, and follow the clues: sunlight, paints and blocking ultraviolet.
- Watch What If? Lab What if concrete could heal its own cracks? Concrete is strong, but it cracks, and water creeping into the cracks can rust the steel inside. Scientists are testing concrete that seals its own cracks, using sleeping bacteria or special lumps of lime. Follow the clues to see what self-healing concrete might change.
For parents & teachers
What children will learn
- Glass is made by melting sand with other ingredients and cooling it quickly.
- Cool glass is hard and brittle; hot glass is soft enough to shape.
- Safety glass is laminated with plastic or tempered so it breaks more safely.
- Glass made thinner than paper can bend.
Recommended ages: 7 to 17 · About 15 minutes
Talk about it
- Where would bendy glass be useful, and where would it be a problem?
- Why do you think car windows and phone screens use special glass?
- What other materials are hard but break easily, and which bend instead?
Try at home or in class
- Go on a glass hunt at home and list where glass is used. Which pieces are thick and which are thin? Look, don't handle: let a grown-up move anything made of glass.
- Thickness test without glass: bend a thick plastic ruler and then a thin strip of plastic from packaging or a sheet of paper. Which bends more easily? Talk about why thin glass can flex.
Key vocabulary: brittle, silica, tempered glass, laminated glass, micrometer, flexible
Where these facts come from
- Glass , Encyclopaedia Britannica
- Safety glass , Encyclopaedia Britannica
- Tin , Royal Society of Chemistry, Periodic Table
- Flexible Glass Could Bring Back the Flip Phone , MIT Technology Review
- SCHOTT UTG in foldable displays , SCHOTT
Checked, not yet human-reviewed. Last updated October 27, 2026. Spotted a mistake? Tell us.