Borosilicate 3.3: Full Technical Specifications

Bottom line. Buyers usually ask "how heat-resistant is it", but what actually determines whether a vessel can be used is a set of interdependent properties: the expansion coefficient governs thermal-shock tolerance, the softening point governs processing and the practical limit, and the hydrolytic / acid / alkali resistance classes govern service life in chemical environments. The value of borosilicate 3.3 is not one outstanding number — it is that this whole set sits at a high level.

[!] Every figure on this page comes from published literature and manufacturers' public technical documentation — not from RichTech measurements. Sources are listed at the foot of the page.

1. Physical properties

Three temperatures, three different meanings — none of them is "the maximum service temperature":

• Strain point 520 °C — near the upper limit for sustained load
• Annealing point 560 °C — the range where internal stress is relieved
• Softening point 820 °C — the temperature at which the glass can be formed

2. Chemical resistance classes

Behind each class there is a number:

• ISO 719 Class 1: 300–500 μm glass grain in water at 98 °C for 1 hour — less than 31 μg Na₂O per gram removed
• ISO 720 Class 1: water at 121 °C for 1 hour — less than 62 μg Na₂O per gram
• DIN 12 116 Class 1: 6 h boiling in 6 N HCl — surface erosion less than 0.7 mg/100 cm²
• DIN ISO 695 Class 2: 3 h boiling in equal volumes of 1 mol/L NaOH and 0.5 mol/L Na₂CO₃ — surface erosion about 134 mg/100 cm²

These figures turn "chemical resistance" from an adjective into a measurable specification. Buyers can ask a supplier for the test basis behind the stated class — this is general procurement advice; what any individual supplier can provide must be confirmed separately.

3. Where the gap actually is

[!] This point must be stated precisely: in the table above, both materials are Class 2 for alkali and both are Class 1 for acid. The real dividing line is hydrolytic resistance — 3.3 is Class 1, soda-lime is Class 3.

So the right question is not "which is more corrosion-resistant", but: which medium (water, acid, alkali), at what temperature, for how long.

4. More than one formulation

Published literature gives at least two typical compositions:

"3.3" defines a coefficient of expansion, not a fixed recipe. Saying "borosilicate 3.3 is made of X" is therefore imprecise; the accurate form is "one published formulation is…".

FAQ

What exactly does 3.3 mean?

It refers to the class with a coefficient of linear expansion of 3.3×10⁻⁶ K⁻¹. ISO 3585 groups borosilicate glasses by expansion coefficient; 3.3 is the most widely used class.

Softening point is 820 °C — can I use it at 800 °C?

No. The softening point is where the material begins to deform significantly; it is a processing parameter, not a service limit. Continuous service temperature depends on the specific product design and wall thickness.

Alkali resistance is only Class 2 — does that mean I cannot use alkali?

It does not mean "cannot be used"; it means the erosion rate is higher than in other media. After prolonged alkali contact, dimensional change or damage to graduations may occur, so long soaking in alkali is not its strength.

Related reading

• Borosilicate 3.3 vs low-borosilicate
• What 280°C thermal shock means
• Why glass resists acid but not alkali