Borofloat 33
ASTM E438 Type I · EN 7080 · GB GB/T 4438 · also Schott Borofloat, Pyrex
Borofloat 33 is a low-expansion borosilicate silicate glass (type 3.3, sold under designations 7080, ASTM E438 Type I, Pyrex, Duran and GB/T 4438) produced as micro-float sheet, with good thermal shock and chemical resistance.
Reference datasheet — Borofloat 33 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed Glass condition
Borofloat 33 tempers and conditions
Borofloat 33 is supplied in 5 conditions, soft to hard. Annealed Glass is the default FabDigit quotes; the values on this page are for it.
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 | |
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 |
Supply forms, finishes and certifications
Ways Borofloat 33 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
G220 | IEC 60672 Type G-220 | Certification |
G231 | IEC 60672 Type G-231 | Certification |
G232 | IEC 60672 Type G-232 | Certification |
What is Borofloat 33?
Borofloat 33 is a low-expansion borosilicate silicate glass (type 3.3, sold under designations 7080, ASTM E438 Type I, Pyrex, Duran and GB/T 4438) produced as micro-float sheet, with good thermal shock and chemical resistance. Engineers specify it for sight glasses, laboratory ware and optical or solar cover plates where a flat, fire-polished sheet is needed to about 450 °C, and it is available annealed as well as heat-strengthened (HS) and tempered. Like all glass it is brittle with low tensile strength (35 MPa) and poor machinability (score 12), so all cutting and drilling must be done before tempering. Fused silica is the alternative when higher service temperature or deep-UV transmission is required. Borofloat 33 has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 85% of glass grades. Borofloat 33 has a tensile strength of 35 MPa (5.08 ksi), weaker than 75% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi).
What is Borofloat 33 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
- Lighting and lamp envelopes
- Anodically bonded sensor caps
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
Borofloat 33 properties
Typical room-temperature values for Borofloat 33-Annealed Glass; bars are the position among glass grades.
Physical4
Borofloat 33 has a density of 2.23 g/cm³ (0.0806 lb/in³), lighter than 85% of glass grades.
Mechanical13
Borofloat 33 has a tensile strength of 35 MPa (5.08 ksi), weaker than 75% of glass grades. Elongation at break is 0% and the elastic modulus is 64 GPa (9.28 Msi).
Thermal5
Borofloat 33 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 58% of glass grades. Thermal expansion is 3.3 µm/m·K (1.81 µin/in·°F).
Electrical5
Borofloat 33 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 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's machinability is not recommended (12/100, worse than 68% 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.
Strength versus weight in the glass family
Yield strength against density for every glass grade FabDigit runs. Borofloat 33 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Borofloat 33
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.
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) |
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.
Equivalent designations
Standards and trade names that resolve to Borofloat 33 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- E438 Type I
- EN / DIN / Werkstoff-Nr.
- 7080
- GB (China)
- GB/T 4438
- Trade names
- Schott BorofloatPyrexDuran
How much does Borofloat 33 cost?
Borofloat 33 is a standard-cost glass ($$), cheaper than about 60% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Borofloat 33 — frequently asked
What is Borofloat 33 used for?
Borofloat 33 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?
Borofloat 33 has a typical tensile strength of 35 MPa (5.08 ksi) — weaker than 75% of glass grades. Strength varies by condition: see the 5 listed tempers.
Is Borofloat 33 easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 68% 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 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?
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 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?
Borofloat 33 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.
How much does Borofloat 33 cost?
Borofloat 33 is a standard-cost glass ($$), cheaper than about 60% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.