In industrial and laboratory settings, the material of choice for glass tubing is often borosilicate. Renowned for its excellent thermal and chemical resistance, borosilicate tubes are crucial in various applications, from sight glasses to high-pressure systems. This article delves into the technical specifications of borosilicate tubes, their applications, and why they are indispensable in many industries.


What is Borosilicate Glass?

Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. It is known for having very low coefficients of thermal expansion (~3 × 10⁻⁶/K at 20°C), making it resistant to thermal shock more than any other common glass. This property makes borosilicate glass ideal for applications involving sudden temperature changes.


Key Properties of Borosilicate Tubes

  • Thermal Resistance:

    Borosilicate glass can withstand high temperatures up to 400°C and sudden temperature changes. This makes it suitable for use in environments where rapid heating and cooling occur.

  • Chemical Durability:

    Borosilicate glass resists chemical corrosion from acids, alkalis, and organic solvents, except hydrofluoric acid, hot concentrated phosphoric acid, and strong alkalis at elevated temperatures.

  • Mechanical Strength:

    While not as strong as some metals or plastics, borosilicate glass has a high tensile strength of approximately 40-120 MPa. Its high resistance to thermal stress enhances its mechanical stability.

  • Optical Clarity:

    It offers excellent transparency and can be manufactured to meet various optical requirements, such as in sight glasses and level gauge glasses.


Applications of Borosilicate Tubes

  • Sight Glasses:

    Used in various industries to view processes within vessels and pipelines without opening them. Borosilicate sight glasses provide clear visibility and withstand harsh environments.

  • Level Gauge Glass:

    Essential in monitoring fluid levels in tanks and boilers. They are designed to endure high pressures and temperatures.

  • Red Line Tubes:

    These tubes feature a red line for enhanced visibility of fluid levels, critical in high-precision applications.

  • High Pressure Tubes:

    Employed in systems where they must endure extreme pressures without compromising integrity.

  • Heavy Wall Sight Glasses and Boiler Glass Tubes:

    These provide additional thickness to withstand higher mechanical stress and thermal shock in boilers and other high-pressure environments.


Circular Sight Glasses

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Technical Specifications

  • Dimensional Tolerances:

    Borosilicate tubes are manufactured with tight tolerances to ensure they fit precise applications. Dimensions can vary based on requirements, ranging from small-diameter tubing for laboratory use to larger diameters for industrial sight glasses.

  • Thermal Expansion:

    As mentioned, borosilicate glass has a low coefficient of thermal expansion, typically around 3.3 × 10⁻⁶/K. This ensures minimal expansion and contraction with temperature changes, maintaining structural integrity.

  • Chemical Composition:

    The typical composition includes about 80% silica (SiO2), 13% boric oxide (B2O3), 4% sodium oxide (Na2O), and 2-3% aluminum oxide (Al2O3). This composition gives borosilicate its unique properties.

  • Mechanical Properties:

    • Density: Approximately 2.23 g/cm³
    • Elastic Modulus: About 63 GPa
    • Poisson’s Ratio: Around 0.2
    • Hardness: Knoop hardness of 480 kg/mm²
  • Optical Properties:

    • Refractive Index: Approximately 1.47
    • Transmission Range: Transmits light from UV to infrared, depending on the thickness and specific composition.


Comparing Borosilicate with Other Glass Types

  • Soda Lime Sight Glass

    While soda lime glass is cheaper and more widely used, it lacks the thermal and chemical resistance of borosilicate. It is suitable for less demanding applications.

  • Tempered Glass

    Tempered glass offers high mechanical strength and safety features but may not match the chemical resistance of borosilicate.


Why Choose Borosilicate Tubes?

Aspect Description
Safety Their high resistance to thermal shock and chemical corrosion ensures safe operation in harsh conditions.
Durability Long-lasting and reliable, reducing the need for frequent replacements.
Versatility Suitable for a wide range of applications, from laboratory use to heavy industrial processes.



Understanding the technical specifications of borosilicate tubes is essential for selecting the right product for your application. Their unique properties make them invaluable in various industries, providing safety, durability, and clarity. Whether you need a sight glass, level gauge glass, or high-pressure tube, borosilicate glass is a robust and reliable choice.

By integrating borosilicate tubes into your systems, you ensure optimal performance and longevity, making them a sound investment for any industrial or laboratory application. Explore the range of borosilicate products from Zight, and discover how our high-quality glass solutions can meet your specific needs.