Borofloat 33 Glass Properties & Finishing Services
Full property data, plus custom cutting, dicing & polishing
Borofloat Glass is manufactured by Schott, and is a highly chemically resistant borosilicate glass with low thermal expansion that is produced using the float method. Other key properties of Borofloat are its mirror like surface quality, high thermal resistance, and excellent transmission.
Borofloat® 33 is a borosilicate glass manufactured by Schott using the float process, prized for its low thermal expansion, high chemical resistance, and excellent optical transmission. Valley Design does not manufacture Borofloat glass — we provide the precision dicing, lapping, and polishing services that turn as-drawn Borofloat sheet into finished wafers, substrates, and custom components to your specification.
Borofloat is often used as a lower-cost equivalent to Pyrex 7740 for many applications. The two materials differ slightly in their alkali ratio (Na2O to K2O) and in minor oxide content, which affects transmission. Made from natural raw materials, Borofloat is free of heavy metals and lead, and is fully recyclable.
Available sizes of Borofloat glass
Borofloat is supplied as sheet glass in standard thicknesses from 0.7mm up through 21mm. Valley Design processes this material into wafers, substrates, and custom components in typical geometries of 1″ square or round, 2″, 3″, 4″ (100mm), 5″ (125mm), 6″ (150mm), 8″ (200mm), and 12″ (300mm). Other dimensions and custom polished thicknesses are available — request a quote for your specification.
Applications of Borofloat glass
Borofloat borosilicate glass wafers and substrates are used across precision engineering and optical applications, including:
- Electrical insulators
- Radiation and neutron-shielding windows (boron content in borosilicate glass formulations is a documented basis for neutron attenuation)
- Vision and cover panels
- Chemical-industry equipment linings
- Biotechnology slides
- Optical filters and telescope mirrors
- Display glass and electronics sensors
- MEMS applications, anodic bonding, and silicon-on-insulator (SOI) processes
Thermal properties of Borofloat 33 glass
| Thermal coefficient of expansion (20–300°C) |
3.25 × 10-6 K-1 |
| Specific thermal capacity (20–100°C) |
0.83 kJ × (kg × K)-1 |
| Thermal conductivity (90°C) |
1.2 W × (m × K)-1 |
| Transformation temperature (Tg) |
525°C |
| Annealing point |
560°C |
| Softening point |
820°C |
| Max. operating temperature, short term (<10 hr) |
500°C |
| Max. operating temperature, long term (≥10 hr) |
450°C |
| Resistance to thermal shock (RTS) |
~160–175 K, depending on thickness |
Mechanical properties of Borofloat 33 glass
| Density (25°C) |
2.2 g/cm3 |
| Young’s Modulus |
64 kN/mm2 |
| Knoop Hardness HK 0.1/20 |
480 |
| Poisson’s Ratio |
0.2 |
| Bending Strength |
25 MPa |
Chemical properties of Borofloat glass
| Hydrolytic resistance |
HGB 1 (per ISO 719) |
| Acid resistance |
Class 1 (per ISO 1776) |
| Alkali resistance |
Class A2 (per ISO 695) |
Material composition of Borofloat glass
| SiO2 |
81% |
| B2O3 |
13% |
| Na2O/K2O |
4% |
| Al2O3 |
2% |
Electrical properties of Borofloat glass
| Dielectric constant |
4.6 @1MHz & 25°C |
| Loss tangent |
37 × 10-4 @1MHz & 25°C |
| Dielectric strength |
16 kV/mm @50Hz & 25°C |
| Electric volume resistivity |
8.0 @250°C, 6.5 @350°C |
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Valley Design’s Borofloat glass finishing services
Valley Design does not manufacture Borofloat glass. Once Schott has produced the as-drawn sheet, Valley Design provides the precision finishing work manufacturers and design engineers need to put it into production, including:
- Lapping and polishing beyond the standard 60/40 scratch/dig, transparent as-drawn finish — up to a low-Angstrom polished surface finish
- Precision dicing to custom die sizes as small as 0.127mm square
- Custom polished thicknesses in wafer diameters up to 300mm (12″)
- Stock availability in standard sizes for fast turnaround, plus custom specifications for prototype and production volumes
If you have Borofloat components that need a tighter surface finish or flatness than standard as-drawn sheet, or you’re specifying a new design, request a quote and our technical team will help scope the work.
Frequently asked questions about Borofloat glass
What is Borofloat glass?
Borofloat is a borosilicate glass manufactured by Schott using the float process. It’s known for low thermal expansion, high chemical resistance, and excellent optical transmission, and is often used as a lower-cost alternative to Pyrex 7740 in applications requiring similar thermal and chemical performance.
Is Borofloat the same as Pyrex?
Not identical, but very similar. Both are borosilicate glasses with comparable thermal and chemical properties and can often be used interchangeably. Borofloat is a sheet glass produced by the float process and typically more cost-effective; Pyrex 7740 is formed in blocks that must be sliced, ground, lapped, and polished to reach a transparent optical finish.
Is Borofloat glass the same as tempered glass?
No. Tempering is a heat or chemical treatment applied to any glass composition to increase its strength and change how it breaks; Borofloat is a specific borosilicate glass composition. Borofloat can be tempered, but as supplied and as used on most of Valley Design’s finished components, it is not.
What is Borofloat glass used for?
Borofloat is used anywhere low thermal expansion and chemical durability matter: electrical insulators, radiation and neutron-shielding windows, vision and cover panels, chemical-processing equipment linings, biotech slides, optical filters, telescope mirrors, display glass, electronics sensors, and MEMS/anodic-bonding applications.
Can Valley Design cut, dice, or polish Borofloat glass to custom sizes?
Yes. Valley Design laps and polishes Borofloat glass beyond its standard as-drawn finish, and dices it to custom die sizes as small as 0.127mm square, in wafer diameters up to 300mm (12″). Request a quote for your specification.
What surface finish and flatness can Valley Design achieve on Borofloat glass?
Standard as-drawn Borofloat ships with a transparent 60/40 scratch/dig finish and flatness around 3–5 waves/inch. Valley Design’s lapping and polishing improves on both, reaching a low-Angstrom surface finish where the application calls for it.
Is Borofloat glass available from Valley Design’s stock?
Yes. Valley Design maintains a rotating stock of Borofloat glass across standard sizes and thicknesses. Stock changes daily to meet demand, so contact our Customer Service team to confirm current availability for your specification, or request a quote for a custom size.
Related Borofloat & borosilicate resources
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