Borosilicate glass: What makes this material so special
Borosilicate glass at a glance
- Designed for extreme conditions. Borosilicate glass 3.3 was developed by Otto Schott in Jena at the end of the 19th century. Its low coefficient of thermal expansion (3.3 × 10⁻⁶/K) makes it resistant to thermal shock: depending on the wall thickness, it can withstand temperature differences from 100 to over 200 °C (Schott AG, DURAN data sheet).
- Lead-free and chemically inert. Unlike many crystal glasses, borosilicate glass contains no lead or heavy metals. It is resistant to acids and alkalis and does not leach any substances into beverages.
- Dishwasher safe. Borosilicate glass can withstand standard dishwashers under normal household conditions permanently without becoming cloudy or dull.
- Demanding to process. Borosilicate glass is processed at a higher temperature range than other types of glass (approx. 825–1260 °C). Its higher viscosity makes it more difficult to blow, especially using freehand techniques.
- Clear disadvantages. Borosilicate glass sounds less brilliant than crystal glass, doesn't achieve the same refractive index, and cannot be processed into such thin walls. It is a specialty glass, not a universal glass.
A material between laboratory and dining table
When people hear "borosilicate," they think of chemistry lessons, laboratory flasks, and Bunsen burners. Hardly anyone thinks of a table set by candlelight.
This material has properties that make it interesting for drinking glasses, properties that no other glass offers in exactly this combination: high thermal shock resistance, chemical neutrality, permanent dishwasher resistance and lightness.
The fact that almost no one drinks from it has a simple explanation: borosilicate glass is significantly more difficult to work with than crystal or soda-lime glass. Most glassworks and manufacturers therefore work with other materials.
This article explains what borosilicate glass is, where its strengths and weaknesses lie, and for whom it is the right choice.
What is borosilicate glass?
At the end of the 19th century, the glass chemist Otto Schott in Jena developed a glass with a high boron oxide content, hence the name. His goal was a material that could withstand extreme temperature fluctuations: a glass for laboratory equipment, industrial applications, and science.
The most important property: Borosilicate glass 3.3 hardly expands when heated. The number 3.3 refers to the coefficient of thermal expansion (3.3 × 10⁻⁶/K), which is about three times lower than that of conventional soda-lime glass (~9 × 10⁻⁶/K). Under normal household conditions, borosilicate glass can withstand temperature differences of 100 to over 200 °C, depending on the wall thickness, without cracking. By comparison, soda-lime glass tolerates a difference of only about 40 °C.
Today, borosilicate glass 3.3 is primarily known as laboratory glassware (brand names like Duran or Pyrex). In the world of drinking glassware, it's a niche, but a growing one: some manufacturers and design brands deliberately choose this material because it offers properties that crystal and soda-lime glass don't.
From the workshop: How borosilicate behaves under a flame
Technical data sheets tell half the story. Only those who work with a material on a daily basis truly know how it behaves.
Master glassblower Eckhard Martin has worked with borosilicate glass for over five decades, exclusively using freehand techniques without molds since 1975. He describes borosilicate as a material with its own rhythm: its higher viscosity demands more patience, and its shorter working window requires more precision.
This is due to physics: glass doesn't have a fixed melting point, but becomes increasingly softer with rising heat. The glassblower works within a wide temperature range, in which the material exhibits varying degrees of viscosity and malleability; for borosilicate, this range is roughly between 825 and 1,260 °C (Schott AG, DURAN guidelines for softening and working point). At every stage, borosilicate is more viscous than crystalline or soda-lime glass; it moves more slowly and cools down faster.
A crucial advantage becomes apparent during finishing work: if something is wrong, the glassblower can selectively reheat and correct the affected area. This is hardly possible with soda-lime glass, where localized heating quickly leads to stress cracks throughout the entire piece. The low coefficient of thermal expansion of borosilicate glass allows heat to be applied locally without affecting the rest of the glass. The glasses still bear the glassblower's signature, as the basic shape must fit within the narrow working window.
Regarding wall thickness: Borosilicate can certainly be worked very thinly; even less than 1 mm is possible. In freehand glassblowing, the typical wall thickness is 1.5–2 mm, because the glassblower works without a mold, and the thicker material is intentionally part of the tactile experience. What is considered elegance in crystal—fragility—becomes substance in borosilicate: a glass that feels secure, that one can grasp without thinking.
Three types of glass compared
Three types of glass dominate the drinking glass market. Since these terms are often unfamiliar, here is a brief explanation:
Crystal glass contains metal oxides (traditionally lead oxide, now also barium or zinc) that give the glass a high refractive index, brilliant sound, and exceptional clarity. Most high-quality wine glasses, champagne flutes, and decorative drinking glasses are made of crystal. According to EU Directive 69/493/EEC, only glass containing at least 24% lead oxide may be called "lead crystal."
Soda-lime glass (also known as ordinary glass or soda glass) is by far the most common type of glass: window panes, bottles, canning jars, and most inexpensive drinking glasses are made from it. It is melted from sand, soda, and lime and is inexpensive to produce.
Borosilicate glass contains a high proportion of boron oxide instead of soda, which gives it significantly higher temperature resistance and chemical resistance. It is primarily known as laboratory and industrial glassware (Duran, Pyrex) and has only been used for drinking glasses for a few years.
|
Characteristic |
Borosilicate glass 3.3 |
crystal glass |
Soda-lime glass |
|---|---|---|---|
|
Thermal shock resistance |
High (100–220 °C depending on wall thickness) |
Low (~40 °C) |
Low (~40 °C) |
|
Dishwasher safe |
Yes, permanently |
Conditional; the surface deteriorates over time. |
Conditional |
|
Lead-free |
Yes, always |
Not always (lead crystal ≥ 24% PbO) |
Yes |
|
Taste neutrality |
Very high, chemically inert |
High |
High |
|
Turbidity resistance |
Very high |
Low to medium |
Medium |
|
Sound when tapped |
Subtle, light |
Brilliant, long-lasting |
Medium |
|
Refraction / Brilliance |
Clear, neutral |
Very high (prism effect) |
Medium |
|
Weight |
Light |
Heavier (due to metal oxides) |
Medium |
|
Price (drinking glasses) |
Medium to high |
High to very high |
Low to high |
|
Availability |
niche |
Widely available |
Very widely available |
Where borosilicate excels: thermal shock resistance, dishwasher compatibility, chemical purity, lightness, and durability. Those who use glasses daily and value durability benefit the most.
Where crystal excels: sound, brilliance, thinness, elegance. For festive occasions, wine tastings, and all those who enjoy the sensory experience of the glass itself, crystal is hard to beat.
Where soda-lime glass excels: price and availability. For restaurants, large gatherings, and uncomplicated everyday use, it's the most pragmatic choice.
Color and borosilicate
A particular advantage of borosilicate glass becomes apparent in color processing. Colored glass can be directly fused into borosilicate; the color becomes part of the material, not a coating or paint.
For this color fusion to work, the colored and transparent glass must have the same coefficient of thermal expansion when cooling. If this coefficient doesn't match, internal stresses arise that can lead to breakage. The uniform coefficient of thermal expansion of borosilicate 3.3 makes this bond more stable than with many other types of glass.
The colors themselves are created by metal oxides: cobalt oxide produces blue, chromium oxide green, copper oxide turquoise, and gold or selenium compounds red (so-called gold ruby or selenium ruby glass). Red is the most complex and expensive glass color because its development is particularly sensitive to temperature and atmospheric fluctuations.
When a glass breaks
No glass is indestructible. But borosilicate glass has a property that other types of glass generally don't offer: it can be repaired by reheating it over a flame. A glassblower can fuse broken pieces and reattach them.
The reason is the same one that also allows for reworking during manufacturing: the low coefficient of thermal expansion allows a fracture point to be heated locally without the rest of the glass cracking due to thermal stress. With soda-lime glass or lead crystal, localized heating quickly leads to stress cracks. Furthermore, soda-lime glass tends to devitrify (crystallize) when reheated, which makes repair even more difficult.
Not an argument for carelessness, but one for longevity.
Which glass suits whom?
The choice of glass material depends on what matters most at the dining table. There is no objectively "best" glass, only different priorities.
Crystal glassware , for when the moment matters. The brilliant sound of a toast, the play of light in the bowl, the delicate elegance in the hand. Crystal enhances the wine and the occasion. The classic choice for festive tables and tastings.
Soda-lime glass : ideal when simplicity is key. Affordable, readily available, and safe to use. The pragmatic choice for restaurants, large gatherings, and everyday use without any fuss.
Borosilicate glass : when character matters. Because it is so demanding to work with, it is almost exclusively shaped freehand by specialized glassblowers, making each piece unique. It is lighter than crystal, displays the wine's color faithfully, and looks as good as new after ten years. The choice for people who want a glass with character, one they can use every day without a second thought.
None of these options is superior to the other. They serve different needs.
Frequently asked questions about borosilicate glass
Is borosilicate glass dishwasher safe?
Yes. Borosilicate glass 3.3 can withstand standard dishwashers under normal household conditions long-term. Its surface is significantly more resistant to glass corrosion (clouding) than crystal or soda-lime glass.
Is borosilicate glass lead-free?
Yes, always. Borosilicate glass contains no lead oxide. This is not guaranteed for crystal glass: According to EU Directive 69/493/EEC, traditional lead crystal contains at least 24% lead oxide. Newer "crystalline" glasses may be lead-free, but this is not necessarily the case.
Can you drink wine from borosilicate glass?
Yes. Borosilicate glass is taste-neutral and chemically inert; it doesn't release any substances into the wine. The disadvantage compared to crystal: the glass sounds less brilliant when clinked and doesn't have the light refraction that visually enhances the wine.
What is the difference between borosilicate glass and crystal glass?
The main difference lies in the composition. Crystal glass contains metal oxides (lead, barium, or zinc) that give it brilliance, sound, and refractive power. Borosilicate glass contains boron oxide, which provides thermal shock resistance and chemical resistance. Crystal is the glass for the moment, borosilicate the glass for everyday use.
Is borosilicate glass shatterproof?
No. No glass is shatterproof. However, borosilicate glass is more resistant to thermal shock than other types of glass; it cracks significantly less often due to temperature fluctuations. Its resistance to mechanical impacts (dropping, bumping) is similar to that of other types of glass.
Why is borosilicate glass so rare in drinking glasses?
Because it is more difficult to process. Borosilicate is processed in a higher temperature range (approx. 825–1,260 °C vs. approx. 700–1,000 °C for soda-lime glass), the viscosity is higher at every stage, and the working window is shorter. Therefore, most glassworks and manufacturers use other materials.
Sources and further information
- Schott AG: Technical data sheet DURAN borosilicate glass 3.3, coefficient of thermal expansion, operating point, softening point. schott.com/duran
- ISO 3585:1998: Specification for borosilicate glass 3.3 (composition, thermal properties)
- EU Directive 69/493/EEC: Definition of crystal glass categories, minimum lead oxide levels. eur-lex.europa.eu
- Glass coloration through metal oxides: cobalt oxide (blue), chromium oxide (green), copper oxide (turquoise), gold/selenium compounds (red). See Wikipedia: Glass coloring and color marking
- Repairability of borosilicate glass: The low coefficient of thermal expansion allows for localized heating without stress cracking. See De Dietrich Process Systems: Repair Options for Borosilicate Glass ; Mountain Glass Arts: Flameworking 101
- Workshop experience: Eckhard Martin, master glassblower since 1975 (quotes from personal conversation)
Read more:
- The art of free glassblowing: 40 minutes per glass
- Wabi-sabi at the dining table: Why imperfect glasses are the more beautiful ones
- The world of glass art: An overview of all techniques
- Eckhard Martin, master glassblower
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