Author: HWS Mainz Laboratory Engineering Team
Published by HWS Mainz – Experts in Custom Glass Reactor Systems for Research and Industry, specializing in borosilicate glass reactors.

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Introduction: The Unsung Hero of Laboratory Equipment

In the age of advanced composites, alloys, and polymers, it might be tempting to view glass as outdated. Yet, for laboratory reactor systems, one material continues to dominate: borosilicate glass 3.3.

From pharmaceutical synthesis to high-temperature organic reactions, chemical engineers across disciplines continue to rely on this versatile material. Why? Because borosilicate 3.3 combines chemical resistance, thermal stability, mechanical strength, and transparency—a combination unmatched by alternatives.

In this post, we explore the science behind borosilicate glass, compare it to other reactor materials, and explain why HWS Mainz continues to rely on Type I, Class A borosilicate glass from Schott for all our precision reactor systems.

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What Is Borosilicate 3.3?

Borosilicate glass 3.3 is a type of technical glass composed primarily of:

• Silicon dioxide (SiO₂): ~80%
• Boric oxide (B₂O₃): ~13%
• Sodium and aluminum oxides: small percentages

The “3.3” refers to its low coefficient of thermal expansion (3.3 × 10⁻⁶/K), which makes it highly resistant to thermal shock.

This unique composition offers properties critical for demanding laboratory applications:

• High transparency
• Excellent thermal resistance
• Broad chemical compatibility
• Dimensional stability
• Long service life

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Thermal Shock Resistance: Operating Through Extremes

One of the greatest threats to glass labware is sudden temperature change. Traditional soda-lime glass can crack when exposed to rapid heating or cooling.

Borosilicate 3.3, however, thrives under these conditions. Its low thermal expansion means it can withstand:

• Direct flame exposure
• Rapid heating to >300°C
• Thermal cycling in jacketed reactors

This is essential for:

• Temperature-controlled reactions in jacketed vessels
• Vacuum distillations
• Crystallizations with heating/cooling ramps

At HWS, our bench-scale and pilot reactors are built with jacketed and triple-walled configurations, designed to support fluid circulation without compromising the integrity of the glass. This is only possible because of borosilicate 3.3’s outstanding thermal resilience.

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Chemical Resistance: A Universal Laboratory Standard

Chemical engineers demand materials that won’t react with their reagents. Borosilicate 3.3 is non-porous and inert to most chemicals, including:

• Acids (HCl, H₂SO₄, HNO₃)
• Alkalis (NaOH, KOH)
• Solvents (toluene, acetone, DCM)
• Aqueous salt solutions and brines

Unlike metals, which may corrode, or plastics, which can absorb solvents or degrade under UV light, borosilicate remains unchanged.

For highly aggressive media, HWS offers additional options:

• Glass-lined steel components
• PTFE-coated flanges and valve parts
• Halogen-resistant seals and joints

Yet the backbone of chemical compatibility remains borosilicate 3.3, providing long-term resistance without leaching, cracking, or fogging.

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Transparency and Visual Process Control

In modern R&D workflows, visibility is more than a convenience—it’s a safety and process optimization tool.

Being able to observe:

• Stirring uniformity
• Color change
• Precipitate formation
• Foaming or gas evolution

…all without interrupting the process saves time and minimizes the risk of contamination. Borosilicate’s optical clarity ensures your team can visually inspect experiments in real-time.

This is particularly important in multi-step synthesis or during scale-up studies, where visual monitoring complements automated sensors.

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How Borosilicate Compares to Other Materials

Property	Borosilicate 3.3	Stainless Steel	PTFE	Quartz Glass
Thermal Resistance	Excellent	Excellent	Fair	Exceptional
Chemical Resistance	Excellent	Moderate	Excellent	Excellent
Pressure Rating	Low–Moderate	High	Low	Moderate
Transparency	Excellent	None	Translucent	Excellent
Price/Availability	Moderate	High	Moderate	Expensive
Customization Flexibility	Very High	Medium	Low	Low

While each material has its place, only borosilicate offers the right balance of performance, safety, and flexibility needed for most laboratory reactor applications.

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HWS Mainz: Precision Reactors in Schott Borosilicate Glass

At HWS, we exclusively use Type I, Class A borosilicate glass from Schott (Mainz)—the global leader in scientific glass. Each piece of reactor glassware we fabricate undergoes:

• Precision shaping and annealing
• Thermal stress testing
• Burned-in serial number & production date

This enables full traceability for quality control, repair, and spare part matching.

From jacketed reaction vessels and filter reactors to pressure-rated glassware and inert-gas ready systems, our engineers work closely with clients to design reactors that perfectly match their operational needs—without compromising on material quality.

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Frequently Asked Questions

Why is borosilicate 3.3 preferred over soda-lime glass?

Soda-lime glass has a higher coefficient of thermal expansion and lower chemical resistance, making it unsuitable for laboratory reactors exposed to heat and aggressive solvents.

Can borosilicate handle vacuum and slight pressure?

Yes. While not designed for high-pressure applications, properly designed borosilicate vessels with spherical flanges or glass-metal reinforcements can withstand vacuum and low-pressure operations.

What if my application involves hydrofluoric acid?

Borosilicate is not resistant to hydrofluoric acid or hot phosphoric acid. For these cases, HWS offers reactors with protective coatings or alternative materials.

Is it possible to order custom dimensions in borosilicate?

Absolutely. HWS specializes in custom reactor systems. We can adapt vessel diameter, jacket type, flange system, or port layout to your process.

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Conclusion: Material Science that Still Sets the Standard

Despite the rise of exotic polymers and metals, borosilicate 3.3 remains the gold standard for laboratory-scale chemical reactor design. Its combination of chemical inertness, thermal shock resistance, visibility, and mechanical integrity makes it ideal for nearly all R&D applications.

At HWS Mainz, we believe your glass reactor should work with your chemistry—not against it. That’s why every system we produce starts with the best borosilicate glass available, shaped with precision, and finished for performance.

If you’re looking for a reactor that performs reliably under demanding lab conditions, and can be customized to your exact needs, start with borosilicate—and finish with HWS.

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Interested in a custom glass reactor for your lab?
Contact our team: info@hws-mainz.de