Borosilicate 3.3 Glass Material Guide
We supply borosilicate 3.3 glass as SCHOTT Borofloat® 33 sheet from 0.70 mm to 25.4 mm thick, then cut, edge, coat or heat strengthen it to your drawing. Low thermal expansion and strong chemical resistance make it a fit for windows that run hot, carry optical coatings or face chemical exposure.
Capabilities
Glass grade
Borosilicate glass 3.3 · SCHOTT Borofloat® 33
Thickness
0.70–25.4 mm (0.028–1.0 in)
Maximum sheet size
2,299 × 1,702 mm (90.5 × 67.0 in) · For 3.30–15.0 mm sheet
Thermal expansion
3.25 × 10⁻⁶ K⁻¹ · 20–300 °C, ISO 7991
Operating temperature
450 °C long-term · 500 °C short-term (<10 h)
Added processes
AR and oleophobic coating · Screen printing, heat strengthening
Gallery
Get a borosilicate glass quote
Send your thickness, size, edge and coating requirements, and we will confirm a workable Borofloat® 33 configuration.
What Borosilicate 3.3 Means
Borosilicate 3.3 is a borosilicate glass with a mean linear thermal expansion of (3.3 ± 0.1) × 10⁻⁶ K⁻¹ between 20 °C and 300 °C, which is where the “3.3” in its name comes from. Its approximate composition is 80.6% SiO₂, 12.5% B₂O₃, 4.2% Na₂O and 2.2% Al₂O₃. Borofloat® 33 sits inside this family at 3.25 × 10⁻⁶ K⁻¹. The name on a drawing matters: flat sheet, tubing and molded parts often come from different 3.3 producers with slightly different data sheets, so we recommend naming the brand when a value is critical to your design.
Low expansion is what lets the glass handle uneven heating. When a window is hot in the center and cooler at a clamped edge, stress builds in proportion to how far the glass tries to grow. Borofloat® 33 grows far less than standard soda-lime float glass, so it tolerates larger temperature differences across the pane. For lamp, oven and sight-glass windows we check two things: the expected temperature gap across the part and the operating ceiling of 450 °C continuous or 500 °C for under 10 hours. Metal frames expand more than the glass, so gaskets and mounts need room for that movement.
Borosilicate Glass Properties
The values below are SCHOTT reference data for Borofloat® 33. They describe the glass itself, not a guaranteed rating for a finished part.
| Property | Value | Condition / standard |
|---|---|---|
| Thermal expansion α | 3.25 × 10⁻⁶ K⁻¹ | 20–300 °C, ISO 7991 |
| Maximum operating temperature | 450 °C / 500 °C | ≥10 h / <10 h |
| Transformation temperature Tg | 525 °C | — |
| Softening point | 820 °C | 10^7.6 dPa·s |
| Density | 2.23 g/cm³ | 25 °C |
| Young’s modulus | 64 kN/mm² | DIN 13316 |
| Knoop hardness | 480 | HK 0.1/20, ISO 9385 |
| Refractive index nd | 1.47140 | 587.6 nm |
| Abbe number νe | 65.41 | — |
| Chemical resistance | Hydrolytic class 1; acid class 1; alkali class A2 | ISO 719/720, ISO 1776, ISO 695 |
Bending strength of 25 MPa (DIN 52292) is a reference value. Impact resistance depends on mounting, panel size, thickness and drilled holes.
Acids and water barely touch it: after 24 hours at 95 °C in 5% HCl, 0.02 N H₂SO₄ or water, weight loss stays below 0.01 mg/cm² with no visible change. Alkalis and fluorides are different. Six hours in 5% NaOH at 95 °C removes 1.1 mg/cm² and leaves white stains, and 10% HF hazes the surface within 20 minutes. If your part sees caustic cleaning or fluoride chemistry, tell us the medium, concentration and temperature.
Strengthening and Finishing Options
Borofloat® 33 can be heat strengthened, but we do not fully temper or chemically strengthen it. Finishing is broader: we apply AR coatings for UV, visible or NIR bands, oleophobic coatings and screen printing, and the glass also serves as a substrate for dichroic, bandpass, NIR and mirror coatings. Sheets can be CNC shaped to any outline, polished to a custom thickness and fitted with VHB gaskets.
Heat strengthening — Available
The low expansion limits how much surface compression thermal processing can build, so heat strengthening is the practical ceiling for this glass. We use it when a window needs more impact margin than annealed sheet.
Full thermal tempering — Not offered
Borofloat® 33 cannot reach a fully tempered state, so it carries no tempered safety-glazing rating. If your application requires tempered glass and runs within its temperature limits, a tempered soda-lime part may be the better route.
Chemical strengthening — Not offered
Ion exchange depends on alkali in the glass, and borosilicate 3.3 contains only about 4% Na₂O. For thin cover parts that need chemical strengthening, aluminosilicate glass is the usual choice.
Sheet Thickness, Tolerance and Other Forms
Thickness tolerance on Borofloat® 33 widens with thickness, from ±0.05 mm on 0.70–2.00 mm sheet to ±1.0 mm at 25.4 mm.
| Thickness range | Standard thicknesses | Tolerance | Maximum sheet size |
|---|---|---|---|
| 0.70–2.00 mm | 0.70, 1.10, 1.75, 2.00 mm | ±0.05 mm | 851 × 1,149 mm (33.5 × 45.25 in) |
| 2.25–2.75 mm | 2.25, 2.75 mm | ±0.1 mm | 851 × 1,149 mm (33.5 × 45.25 in) |
| 3.30–6.50 mm | 3.30, 3.80, 5.00, 5.50, 6.50 mm | ±0.2 mm | 2,299 × 1,702 mm (90.5 × 67.0 in) |
| 7.50–13.0 mm | 7.50, 9.00, 11.0, 13.0 mm | ±0.3 mm | 2,299 × 1,702 mm (90.5 × 67.0 in) |
| 15.0–16.0 mm | 15.0, 16.0 mm | ±0.4 mm | 15.0 mm: 2,299 × 1,702 mm; 16.0 mm: 851 × 1,149 mm |
| 19.0–25.4 mm | 19.0 / 25.4 mm | ±0.5 / ±1.0 mm | 1,725 × 1,300 mm (67.9 × 51.2 in) |
Where a design falls between standard thicknesses, we can polish sheet down to a custom thickness. Round and curved parts often start from another form. We supply borosilicate tubing from 2 mm OD with standard wall up to 425 mm OD with heavy wall, rod from 2 to 12.5 mm and from 38 mm upward, and molded or pressed borosilicate in spherical, aspherical, cylindrical and flat shapes. A drawn or molded blank avoids machining a dome, lens or cylinder out of thick plate.
Where We Use Borosilicate 3.3
High-temperature lighting and appliance windows
Lamp covers, high-temperature lighting and oven windows depend on the operating ceiling and on the temperature difference across the pane. For these parts we look at thickness and mounting first, then decide whether heat strengthening adds useful impact margin. Screen printing can add borders or markings on the same sheet. Because full tempering is not available, parts that must carry a tempered safety rating need a different glass.
Sight glass, view ports and chemically resistant windows
Process sight glasses and view ports combine heat, chemicals and clamping loads. Borofloat® 33 handles acids and hot water well, while strong alkalis and fluorides attack it, so the process medium decides whether it is suitable. Thick sheet up to 25.4 mm and VHB gasketing are both available for these windows. Pressure ratings depend on your window design and mounting, so we work from your housing drawing.
Optical windows, filters and coating substrates
High transmission across the UV, visible and IR ranges, together with low inherent fluorescence and a low solarization tendency, makes Borofloat® 33 a common optical substrate. We use it for AR-coated windows and as the base for dichroic, bandpass, NIR and mirror coatings. For coated optics, specify the wavelength band, which faces are coated, and the clear aperture.
3D printer beds and micro slides
Printer beds cycle between room temperature and heat on every build, so low expansion helps the plate stay flat and stable. We cut beds to the platform size from standard sheet; tell us the bed’s operating temperature and whether it needs a coating. Micro slides sit at the thin end: 0.70 mm and 1.10 mm sheet both hold ±0.05 mm thickness tolerance.