Borofloat 33 Tempered
Heat-treated state
ASTM E438 Type I · EN 7080 · GB GB/T 4438 · also Schott Borofloat, Pyrex
Pick for safety glazing, sight glasses and pressure windows needing high bending strength and dicing fracture behaviour; no cutting or drilling after tempering.
Values for the Tempered condition
Other Borofloat 33 tempers and conditions
Borofloat 33 is listed in 5 conditions; see the grade overview at Borofloat 33.
- Annealed Glass
- E438-I-A
- HS
- Tempered
- CS
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed GlassDefault as-drawn float, stress relieved | Standard supply state: best optical flatness and free cutting/grinding after supply, but lowest allowable bending stress. | — | 35 | 0 | 480 HV | 1 W/m·K |
ASTM E438 Type I Class A | The laboratory-apparatus classification that Borofloat 33 / Duran / Pyrex 7740 meets: low-expansion borosilicate with CTE ≈ 3.3 ppm/K, hydrolytic class 1 and excellent thermal shock resistance. | — | 35 | — | 480 HV | 1 W/m·K |
Heat-strengthened | Choose when roughly 2–3× the annealed bending strength is needed but large fragment size / low distortion is still required. | — | 70 | 0 | 480 HV | 1 W/m·K |
TemperedThis page thermally toughened (DIN EN 13024) | Pick for safety glazing, sight glasses and pressure windows needing high bending strength and dicing fracture behaviour; no cutting or drilling after tempering. | — | 120 | 0 | 480 HV | 1 W/m·K |
Chemically strengthened | Use for thin sections (<2 mm) or complex shapes where thermal tempering is impossible and flatness must be preserved. | — | 150 | 0 | 520 HV | 1 W/m·K |
What is Borofloat 33 Tempered?
Borofloat 33 Tempered is Borofloat 33 heat treated to Tempered — pick for safety glazing, sight glasses and pressure windows needing high bending strength and dicing fracture behaviour; no cutting or drilling after tempering. Borofloat 33 Tempered has a tensile strength of 120 MPa (17.4 ksi), stronger than 83% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi). Borofloat 33 Tempered has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 85% of glass grades. Annealed Glass is the default condition FabDigit quotes; Tempered is available on request or by drawing note.
Advantages
- Lightweight — 2.23 g/cm³ (0.0806 lb/in³), better than 85% of glass grades
- Low embodied carbon — 1.8 kg CO₂/kg, better than 85% of glass grades
- Good corrosion resistance — 92/100, better than 81% of glass grades
Limitations
- Difficult to machine — 0/100, worse than 100% of glass grades
- Limited service temperature — 300°C (572 °F), worse than 80% of glass grades
Borofloat 33 Tempered properties
Typical room-temperature values for Borofloat 33 Tempered; 14 are specific to this condition. Other listed values are Borofloat 33 reference data and may not represent this condition. Bars are the position among glass grades.
Physical4
Borofloat 33 Tempered has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 85% of glass grades.
Mechanical13
Borofloat 33 Tempered has a tensile strength of 120 MPa (17.4 ksi), stronger than 83% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi).
Thermal5
Borofloat 33 Tempered is rated for continuous service to 300°C (572 °F). It conducts heat at 1.2 W/m·K (0.693 BTU/hr·ft·°F), worse than 58% of glass grades. Thermal expansion is 3.3 µm/m·K (1.81 µin/in·°F).
Electrical5
Borofloat 33 Tempered is an electrical insulator with a dielectric strength of 30 kV/mm (762 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (92/100), better than 81% of glass grades.
Sustainability4
Producing a kilogram of Borofloat 33 Tempered takes about 25 MJ of energy and emits 1.8 kg of CO₂ — less than 88% of glass grades. Typical recycled content is 10%.
Manufacturability2
Borofloat 33 Tempered's machinability is not recommended (0/100, worse than 100% of glass grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Borofloat 33 Tempered
Is Borofloat 33 easy to machine?
Cold-work only with diamond tooling and copious water — core drilling, grinding, waterjet or CO2/femtosecond laser; always edge-seam and anneal-check after cutting, and never cut after tempering.
Can Borofloat 33 be welded?
No fusion welding as such; joined by flameworking/fusion sealing to matched 3.3 borosilicate, or by anodic bonding to silicon, frit sealing and glass-to-Kovar seals thanks to the matched CTE.
Can Borofloat 33 be formed, bent or molded?
Supplied as micro-float sheet; secondary shaping by slumping/bending near the 820 °C softening point, followed by controlled annealing around 560 °C to relieve stress.
What surface finishes work on Borofloat 33?
Fire-polished as-supplied surfaces need no work; edges can be ground/polished, and surfaces accept AR, ITO, metal and hydrophobic coatings, acid etching or sandblasting.
Borofloat 33 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| B2O3gives low CTE, 3.3 class | 12 – 13.5 | 13 |
| Na2ONa2O+K2O ≈ 4 % | 3 – 4.5 | 3.5 |
| K2O | 0 – 1 | 0.5 |
| Al2O3improves durability | 2 – 2.5 | 2 |
| SiO2network former | ≥ 78 (balance) | — |
Borofloat 33 Tempered — frequently asked
What is Borofloat 33 Tempered used for?
Borofloat 33 Tempered is typically used for laboratory glassware and sight glasses, solar panel cover plates, furnace and oven viewing windows, microfluidic and MEMS wafer substrates, optical filter and mirror substrates and lighting and lamp envelopes. In short: borosilicate optical plate.
What is the tensile strength of Borofloat 33 Tempered?
Borofloat 33 Tempered has a typical tensile strength of 120 MPa (17.4 ksi) — stronger than 83% of glass grades. Strength varies by condition: see the 5 listed tempers.
Is Borofloat 33 Tempered easy to machine?
Not especially — machinability is rated not recommended (0/100, worse than 100% of glass grades). Cold-work only with diamond tooling and copious water — core drilling, grinding, waterjet or CO2/femtosecond laser; always edge-seam and anneal-check after cutting, and never cut after tempering.
Can Borofloat 33 Tempered be welded?
No fusion welding as such; joined by flameworking/fusion sealing to matched 3.3 borosilicate, or by anodic bonding to silicon, frit sealing and glass-to-Kovar seals thanks to the matched CTE.
What surface finishes work on Borofloat 33 Tempered?
Fire-polished as-supplied surfaces need no work; edges can be ground/polished, and surfaces accept AR, ITO, metal and hydrophobic coatings, acid etching or sandblasting.
Can Borofloat 33 Tempered be formed, bent or molded?
Supplied as micro-float sheet; secondary shaping by slumping/bending near the 820 °C softening point, followed by controlled annealing around 560 °C to relieve stress.
What is the maximum service temperature of Borofloat 33 Tempered?
Borofloat 33 Tempered is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- BOROFLOAT 33 — Technical Data / Optical, Mechanical, Thermal & Electrical Properties — SCHOTT AG (2023)
- ISO 3585 — Borosilicate glass 3.3, properties — ISO (1998)
- ASTM E438 Type I Class A borosilicate glass — ASTM (2021)
- ASM Engineered Materials Handbook Vol. 4 — Ceramics and Glasses — ASM International (1991)
- DIN EN 1288-5 / DIN EN 13024 — bending strength and thermally toughened borosilicate safety glass — DIN/CEN (2011)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.