Soda Lime Glass vs. Borosilicate Glass

Glass is amazing. It lets us see through walls via window panes. It lets us see things incredibly far away and impossibly small by providing the lenses for telescopes and microscopes.

Even today, glass is helping us usher in tomorrow by being the main component of fiber optic technology. So why do we know so little about this marvelous material that has become a major building block of civilization?

It’s because we take glass for granted. We are so used to looking through glass that we rarely look at it.

There are many different kinds of glass in use nowadays. Laminated glass, tinted glass, mirrored glass, tempered glass, and stained glass, to name a few.

But do you know the two main classifications of glass used in science and industry? Try your luck:

  1. Float glass for windows / Molded glass for drinking glasses?
  2. Clear glass for soda bottles / Amber glass for beer bottles?
  3. Soda lime glass for kitchens / Borosilicate glass for labs?

The correct answer is 3, Soda-lime glass and borosilicate glass is two very different types of glass that share the same DNA.

Window panes, drinking glasses, milk bottles, soda bottles, and eyeglasses are all made of soda lime glass, the household glass that comprises 90% of the glass on our planet.

Laboratory beakers, test tubes, and bottles that are exposed to temperature extremes are generally made of borosilicate glass. It’s an engineered glass, updated for new applications.

For example, a borosilicate glass dish can be taken from a 340-degree oven and plunged into cold water without cracking.

If you try doing that with a common glass dish, you know what happens. It goes kablooey. So, borosilicate glass is a better, stronger version of soda lime glass.

But how much better? And where did borosilicate glass come from? For that matter, where does soda lime glass come from?

Soda Lime Glass is Hundreds of Years Old

Glass, as we know it, has been manufactured for the past 6,000 years.

Like many of the best things in life, glass was discovered by accident. The first glass objects recorded by archeologists were glass beads dating back to ancient Egypt. They were likely the by-products of the crude glazing process Egyptians used to coat pottery.

soda lime glass

About 250 years ago, glassmakers in Europe started adding Sodium carbonate (Na2CO3), commonly known as “soda,” to strengthen the glass.

Thus, soda lime glass was born. It became the cornerstone of our urban infrastructure. It became artsy and trendy.

Most people know that glass is made out of the sand. Did you know it takes a scorching 3090º F to melt a handful of beach sand into glass?

Borosilicate Glass Was Invented in 1882

A German pharmacist named Otto Schott is credited with inventing borosilicate glass in 1882. By simply adding the element Boron to the mix, Schott discovered glass that was not affected by extreme temperatures.

Borosilicate Glass Mug

But it wasn’t exactly a “Eureka!” moment. Soda-lime glass already contained Boron. He just tweaked the amount of Boron in his glass to make it a super-glass.

Here are the four components shared by both borosilicate glass and old-fashioned soda lime glass:

  • Silicon Dioxide SiO2
  • Boron Trioxide B2O3
  • Sodium Oxide Na2O
  • Aluminum Oxide Al2O3

So it is the proportion of each of these elements that makes the difference. Borosilicate glass has more silicon dioxide and Boron than soda lime glass.

In any case, this spurred a glass-making Renaissance in the early 20th century.

Pyrex Enters the Scene in 1914

The next milestone in the history of borosilicate glass came in 1914. That’s when a researcher at Corning Glass named Jesse Littleton listened to his wife’s advice and a new use for borosilicate glass was found!


Littleton was tasked with finding practical uses for the new heat-resistant glass, to no avail. In the meantime, his wife was experimenting in their kitchen with glass samples she appropriated from her husband’s briefcase.

She thought the newfangled glass was 10 times better than her old ceramic casserole dish.

Mrs. Littleton had discovered a secret that spawned a new industry – Pyrex glass cookware.

What Makes Borosilicate Glass So Heat-Resistant?

We’ll have to revisit an advanced Physics lecture to examine the heat-resistant properties of borosilicate glass, so put on your thinking caps.

First, let’s look closer at the kablooey factor. Whenever hot glass comes in contact with cold water or a cold surface, the hot part expands while the cold part contracts. Scientists call this thermal shock.

Coincidentally, consumers and home cooks also call it a shock when glassware explodes. It happens because regular soda lime glass has a high coefficient of thermal expansion. In other words, it expands and shrinks a lot.

When Otto Schott added more Boron to the mix back in 1882, there was no way of knowing how important and enduring borosilicate glass would become.

With a lower thermal expansion rating, borosilicate glass can go from the oven to the freezer with no cracking. That’s exactly what Schott was going for in the 1890s.

He solved the persistent problem of his day by decreasing the thermal expansion coefficient.

In his case, he was trying to develop a glass to cover the street lights of the time. He needed something that could handle the intense heat of the primitive street lights – coupled with the cold, hard rain pelting the outside glass.

Pyrex Jumps the Shark in 1998

For decades, the miracle of Pyrex gave every homemaker the feeling that they could bake anything, cook anything and do anything with Pyrex.

Who can forget the heavy, thick-walled Pyrex measuring cup in almost every kitchen?

It embodied quality and trust, like an old family friend.

Sorry, those days are gone.

Wait, what?

It’s true. Since 1998 Pyrex has been making their glassware out of soda lime glass. Yup, the same glass you have in your lightbulbs. How can that be? (I don’t want to live in a world without borosilicate Pyrex!!!);

Corning sold the brand 25 years ago…quietly. The new owners decided to cut corners in the most flagrant act of “stagflation” ever seen. They kept the price the same but replaced the legendary borosilicate glass with…junk.

They continued making the same claims about their products being heat-resistant and impervious to thermal shock. It’s special glass, they boasted. Tempered glass. Fancy glass.

However, it’s still good old soda lime silica glass. To be fair, modern Pyrex products are still tempered like in the old days.

They still handle temperature extremes like a boss. Do they have the super strength of the old Pyrex formulation?

Not so much.

What Makes Borosilicate Glass So Darn Strong?

In order to understand how much stronger and tougher borosilicate glass is, we must use the scientific scale of mineral hardness.

It’s called the Mohr Scale. Ranging from a 1 for chalk to a 10 for diamonds, it can measure precisely how hard any mineral is.

Soda Lime glass registers a 6.0 on the Mohr Scale; borosilicate glass clobbers it with a 7.5 rating. That means it’s 15 times harder than regular glass.

How Can You Tell the Difference?

There are three ways to test your glass for borosilicate properties.

Look at the edges and rims of the glassware

soda lime glass flat

The rims of borosilicate glassware will be clear and colorless. Soda lime glassware rims appear tinted with blue or green.

Consider the source

If it’s Pyrex, find out what year it was manufactured or purchased. If not, check the manufacturer’s specs. Only buy borosilicate glass from people you trust.

Drop it like it’s hot

Test for hardness to be 100% certain. Knock the plate or platter off the kitchen counter onto the floor.

If it bounces up unscathed, it’s genuine borosilicate glass. If it smashes into pieces, oh well, you can live without that cheap piece of soda lime glassware, right?

Can You Really Make Glass from Beach Sand?

Yes, any beach sand will melt into glass IF HEATED TO 3090º Fahrenheit. It would require a furnace or kiln. All beach sand contains silica, the main ingredient of soda lime glass.

If you took molten sand and poured it onto a red-hot metal plate, the result would be a super transparent, super shiny, and super smooth glass plane on both sides.

I have just described the process known as float glass, the standard way window panes and mirrors have been manufactured for eons.

If it’s so easy to melt sand into glass, why does it not occur naturally? The sun beats down on the sand relentlessly from sunup to sundown, so where’s the glass?

For one thing, the temperature of beach sand never comes close to 3090º F. It may feel like it when you’re barefoot on the burning sand, but it’s not red hot.

There is one naturally occurring phenomenon that tops 4000º F and turns sandy beaches into glass.

It’s lightning. When lightning touches down on a beach, it turns the sand into glass beads instantly.

Borosilicate Glass is Our Future

New uses for borosilicate glass are emerging every year. Indeed, it seems like the 19th Century discovery is still way ahead of our technology, patiently waiting for us to catch up.

Space Module Glass

Aircraft cockpit

Even though borosilicate glass was discovered before the Wright Brothers ever took flight, it is to this day the only material strong enough for aircraft and spaceship lenses.

Silicon Chips

Wirebonding a silicon semiconductor chip

A hundred years before the advent of the personal computer, Otto Schott paved the way for Silicon Valley with an engineered glass that is now indispensable in producing “chips” for electric cars and smart devices. (Notice the similarity between silica and silicon.)

Nuclear Containment

Physicist Albert Einstein was only 3 years old when borosilicate glass was discovered, yet to this day it is one of the few materials approved for use in nuclear plants. It’s the only thing guaranteed to contain waste and prevent liquid leaks.

3D Printing

Heart printed on 3d printer

In the future, 3D Printers using fused deposition modeling will dominate the market. They are heavily dependent on borosilicate glass to cool the extruded plastics.

Which is Better for The Environment?

Which glass is better for the planet, borosilicate or soda lime? The answer is clear, they both are!

Glass is a perfect “green” material for a cleaner environment. It is readily available and recycles like a dream. Not so long ago, glass bottles held the promise of sustainable use.

Glass bottles for recycling

Then we abandoned glass, or rather, the bottling industry abandoned glass. You may remember the golden age of glass when consumers brought back their empty soda bottles in exchange for a discount on a new 6-pack.

Companies didn’t melt down the bottles to form new glass bottles. They power-washed the old “empties” that consumers returned. Then they refilled them with new product. No huge energy investment to recycle glass bottles in the past.

Then someone had the bright idea of bottling soda and milk in plastic bottles. Big mistake! Plastic is made from petroleum, which is hard to find and increasingly more expensive. Glass is made from sand, which is not hard to find at all.

It appears that the world is finally coming to its senses with glass bottles. Consumers are so tired of single-use plastic waste that they are rapidly switching to re-usable borosilicate glass bottles.

These unbreakable glass bottles give you 100% PURE taste with no chemicals or BPA leeching in.

They are good for your health and good for the environment. In fact, anytime you use any type of glass instead a synthetic material, it’s a win-win for the planet.

Isn’t Borosilicate Glass More Expensive Than Soda Lime Glass?

Yes, it is. You get what you pay for. Borosilicate glass water bottles are three or four times more expensive than regular reusable glass bottles. Sheets of borosilicate glass used in lab experiments can cost 10 or 15 times more than soda lime glass.

But borosilicate glass products can last forever. In conclusion, we owe a debt of gratitude to glass.

Soda-lime glass has helped our civilization get to where we are now, and borosilicate glass will help us get through the future. It’s too bad everything in life isn’t as smooth as glass.

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