Borofloat 33 · heat-treated state · default condition
Borofloat 33 Annealed Glass
Properties of the Annealed Glass condition, compared with the other Borofloat 33 tempers.
Standard supply state: best optical flatness and free cutting/grinding after supply, but lowest allowable bending stress.
What is Borofloat 33 Annealed Glass?
Borofloat 33 Annealed Glass is Borofloat 33 heat treated to Annealed Glass — standard supply state: best optical flatness and free cutting/grinding after supply, but lowest allowable bending stress. Borofloat 33 Annealed Glass has a tensile strength of 35 MPa (5.08 ksi), weaker than 80% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi). Borofloat 33 Annealed Glass has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 84% of glass grades.
Advantages
- Low embodied carbon — 1.8 kg CO₂/kg, better than 86% of glass grades
- Lightweight — 2.23 g/cm³ (0.0806 lb/in³), better than 84% of glass grades
- Good corrosion resistance — 92/100, better than 79% of glass grades
Borofloat 33 Annealed Glass properties
Typical room-temperature values for Borofloat 33 Annealed Glass — 4 properties are specific to this condition; the rest are grade-level values shared by every Borofloat 33 temper. Each bar shows where the value sits among the glass grades in FabDigit's library — further right is higher.
Physical4
Borofloat 33 Annealed Glass has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 84% of glass grades.
Mechanical12
Borofloat 33 Annealed Glass has a tensile strength of 35 MPa (5.08 ksi), weaker than 80% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi).
Thermal5
Borofloat 33 Annealed Glass is rated for continuous service to 450°C (842 °F). It conducts heat at 1.2 W/m·K (0.693 BTU/hr·ft·°F), worse than 60% of glass grades. Thermal expansion is 3.3 µm/m·K (1.81 µin/in·°F).
Electrical5
Borofloat 33 Annealed Glass 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 79% of glass grades.
Sustainability4
Producing a kilogram of Borofloat 33 Annealed Glass takes about 25 MJ of energy and emits 1.8 kg of CO₂ — less than 89% of glass grades. Typical recycled content is 10%.
Manufacturability2
Borofloat 33 Annealed Glass's machinability is not recommended (12/100, worse than 65% of glass grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Borofloat 33 tempers and conditions
Borofloat 33 is also supplied in 7 other conditions. The full side-by-side table is on the Borofloat 33 overview.
- Annealed GlassDefaultStandard supply state: best optical flatness and free cutting/grinding after supply, but lowest allowable bending stress.35 MPa tensile
- G220Borosilicate 3.3 supplied to the IEC 60672-3 G-220 ceramic/glass insulating-material class: hydrolytic class 1 chemical durability with standard low-expansion borosilicate thermal and mechanical behaviour.35 MPa tensile
- G231Low-alkali borosilicate variant classified as IEC 60672-3 G-231 for low-loss RF and microwave insulation; reduced dissipation factor and slightly lower permittivity than general-purpose borosilicate.35 MPa tensile
- G232Borosilicate insulating glass qualified to IEC 60672-3 class G-232 for high-voltage duty: high volume resistivity and dielectric strength with low-expansion borosilicate thermal shock resistance.35 MPa tensile
- E438-I-AThe 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 MPa tensile
Working with Borofloat 33 Annealed Glass
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 Annealed Glass — frequently asked
What is Borofloat 33 Annealed Glass used for?
Borofloat 33 Annealed Glass 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 Annealed Glass?
Borofloat 33 Annealed Glass has a typical tensile strength of 35 MPa (5.08 ksi) — weaker than 80% of glass grades. Strength varies by condition: see the 8 listed tempers.
Is Borofloat 33 Annealed Glass easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 65% 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 Annealed Glass 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 Annealed Glass?
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 Annealed Glass 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 Annealed Glass?
Borofloat 33 Annealed Glass is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Borofloat 33 Annealed Glass?
Yes — Borofloat 33 Annealed Glass is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
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.