Optics made of Borofloat
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High-quality borosilicate glass from SCHOTT

Special Properties

  • High transmission of visible and infrared light
  • High operating temperature range:
    - up to 450 °C at permanent load
    - up to 500 °C at temporary load (< 10 h)
  • High UV-transparency
  • Excellent chemical resistivity against strong acids,
    bases, and organic substances
  • Low thermal coefficient of expansion similar to that of silicon wafers used for anodic bonding processes
  • High thermal shock resistivity
  • Clear, practically colorless appearance
  • Low self-fluorescence
  • Relatively low alkali content in the glass composition
  • Low specific weight
  • High scratch and abrasion resistance
  • High elasticity and mechanical strength
  • Superior flatness resulting from a unique micro float manufacturing process

Typical Applications

  • Optics for increased operating temperatures
  • Medical and biotechnology applications
  • Wafer glass for anodic bonding processes
  • Flat glass substrate for dielectric filters
  • Glass components for lighting systems
  • Front glass for high power floodlights
  • Substrates for lighting filters
  • Photovoltaic applications
  • Sight glass windows
  • Fiber optic applications
  • Glass covers for sensors
  • Laboratory glass equipment
  • Glass components for environmental technology
  • Microscope slides for chemical analysis or medical purposes
  • Substrate glass for electronics
  • Laser applications
  • Windows used in harsh environments
  • Neutron absorbers
  • Glass packaging for optoelectronic components
  • Analytic systems
  • Measuring and sensor devices

Related glass types

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48h-Express Service for custom optics Also available in 48 h Express-Service

BOROFLOAT® is a high-quality, clear-transparent glass that offers an excellent and uniform optical transmission from the visible to the infrared spectral range. Thanks to SCHOTT's unique microfloat manufacturing process the borosilicate glass is characterized by superb evenness, high surface quality, low micro roughness, as well as outstanding material homogeneity. Furthermore, BOROFLOAT® glass has a low self-fluorescence over a broad light spectrum.

For a flat-glass, BOROFLOAT® offers an exceptionally high optical quality, which facilitates a full scope of applications in the field of industrial optics, optoelectronics, photonics, analytics, and lighting technology. Hence, in many cases it is used as a base glass for optics without the requirement of expensive additional mechanical polishing processes. SCHOTT's BOROFLOAT® flat glass offers capabilities required by substrate materials used for coated optics like mirrors, filters, anti-reflection coatings, or sometimes even laser optics. It is an ideal choice for the production of window optics, substrates, glass wafers, and other plane optical components. BOROFLOAT® is also well suited for lighting technology and numerous applications in electronics. We, for example, use BOROFLOAT® glass as a coating substrate for our heat-filter products like our cold mirror and hot mirror series which both belong to the category of lighting filters. Also, we use it as glass substrate for our high reflection dielectric mirror optics.

Due to its thermal capabilities, BOROFLOAT® has proven to be perfect and economical material for many glass applications at increased operating temperatures. It is heat-resistant and can permanently be used at temperatures up to 450 °C. In the short term (< 10 h) the glass even withstands temperatures of up to 500 °C. BOROFLOAT® has a low coefficient of thermal expansion close to that of silicon which allows glass-wafers made of SCHOTT's borosilicate glass to be used for anodic bonding applications. BOROFLOAT® has almost the same thermal expansion and mechanical density as PYREX® glass, which was a standard material for the production of glass wafers for a long time. BOROFLOAT® is therefore frequently used today for glass wafers as a substitute glass forPYREX®, which was discontinued many years ago.


SCHOTT Borofloat glass window for a measuring device
nullspacer Figure: CNC-manufactured high-temperature window optics for a micro-reactor made of BOROFLOAT® glass from SCHOTT.


BOROFLOAT® glass has practically the same glass composition as DURAN® which is also a SCHOTT product and that is mainly used for laboratory equipment. Consequently, the glass is very resistant against water, neutral, saline, and acidic solutions as well as to iodine, chlorine, bromine, and organic substances, even over long periods and at temperatures higher than 100 °C. BOROFLOAT® exceeds the chemical strength of many other glass materials and also of most metals. Acids and alkalis can only dissolve small amounts of ions from BOROFLOAT® glass. Therefore, the measurement results are not falsified when BOROFLOAT® is used in analytical technology, as is often the case with conventional soda lime float glass materials. In many cases, these properties enable the use of BOROFLOAT® glass in medical technology and analytical applications. Also, the mechanical properties of BOROFLOAT® glass exceed those of soda-lime glass and even most other borosilicate glass materials. The abrasion resistance of BOROFLOAT® significantly surpasses the one of ordinary soda-lime float glass.

We manufacture all kinds of glass parts from BOROFLOAT®. If you have any question regarding our manufacturing capabilities, please do not hesitate to contact us. To get a quotation for a window, substrate, or any other component made of original SCHOTT BOROFLOAT® 33 glass with individual dimensions please use the button below:


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48h-Express Service for custom optics (Glass thicknesses that are available as part of the high speed express service are marked in the thickness table on this website.)


Note: Further SCHOTT glass materials like the brand glasses MEMpax®, ultrathin D263 T glass, AF 45, AF 32® eco, ultra-thin AS 87 eco, N-BK7, SUPREMAX®, DURAN®, and ZERODUR® transparent glass ceramic are part of the extensive glass delivery program of our company. Please follow the links or contact us for further information about these SCHOTT glass products.


BOROFLOAT® 33 is a registered trademark of SCHOTT.




BOROFLOAT®, 2 mm thick, UV-VIS-IR

SCHOTT BOROFLOAT® Glass, transmission curve UV-VIS-IR

UV-VIS-IR transparency of BOROFLOAT® glass at 2 mm thickness

BOROFLOAT®, 0,70 mm thick, UV

SCHOTT BOROFLOAT Glass UV-transmission curve at 0,7mm thickness

Ultraviolet transparency of BOROFLOAT® glass at 0,70 mm thickness

BOROFLOAT®, 3,30 mm thick, UV

SCHOTT BOROFLOAT Glass, UV-transmission curve at 3,3mm thickness

Ultraviolet transparency of BOROFLOAT® glass at 3,30 mm thickness

Please contact us for measured transmittance curves of other thicknesses.

Optical Properties

  • Abbe constant ve: 65,41
  • Dispersion nF - nC : 71,4 x 10-4
  • Stress optical coefficient K: 4,0 x 10-6 mm2 N-1

Index of Refraction


Wavelength (nm)

Refractive Index


Mechanical Properties

  • Density: 2,2 g/cm3 (25 °C)
  • Young's modulus E: 64 kN/mm2
    (according to DIN 13 316)
  • Poisson's ratio μ: 0,2 (according to DIN 13 316)
  • Shear modulus σ: 25 MPa
    (according to DIN 52 292 T 1)
  • Knoop hardness HK0,1/20: 480
    (according to ISO 9385)

Thermal Properties

  • Coefficient of thermal expansion:
    3,25 x 10-6/K (20-300 °C) (according to ISO 7991)
  • Specific heat capacity cP: 0,83 kJ (kg x K)-1
  • Specific heat conductivity:
    1,2 W (m x K)-1 (90 °C)
  • Transformation temperature Tg: 525 °C
  • Viscosities:
    • Working Point (104 dPa): 1270 °C
    • Softening Point (107,6 dPa): 820 °C
    • Annealing Point (1013 dPa): 560 °C
    • Strain Point (1014,5 dPa): 518 °C
  • Maximum operating temperatures σmax :
    (only valid considering the following RTG and RTS values)
    • for short-term load 500 °C (< 10 h)
    • for long-term load 450 °C (≥ 10 h)
  • Resistance to thermal gradients (RTG):
    • 110 K (< 1 h)
    • 90 K (1-100 h)
    • 80 K (> 100 h)
      (Testing method description on demand)
  • Resistance to thermal shock (RTS):
    • 175 K (at thickness ≤ 3,8 mm)
    • 160 K (at thickness = 5,0-5,5 mm)
    • 150 K (at thickness = 6,5-15,0 mm)
    • 125 K (at thickness > 15,0 mm)
      (Testing method description on demand)

Chemical Properties

  • Hydrolytic resistance:
    • Class HGB 1
      (according to ISO 719 / DIN 12 111)
    • Class HGA 1
      (according to ISO 720)
  • Acid resistance:
    • Class 1 (according to ISO 1776 / DIN 12 116)
  • Alkali resistance:
    • Class A2 (according to ISO 695 / DIN 52 322)

Chemical Glass Composition

  • 81% SiO2
  • 13% B2O3
  • 4% Na20 / K2O
  • 2% Al2O3

Chemical Durability


Reaction time/

Weight loss

5 Vol.-% HCl
24 h at 95 °C
0,02 n H2SO4
24 h at 95 °C
24 h at 95 °C
5% NaOH
6 h at 95 °C
0,02 n NaOH
6 h at 95 °C
0,02 n Na2CO3
6 h at 95 °C
10% HF
20 min at 23 °C
10% NH4F x HF
20 min at 23 °C

Electrical Properties

  • Dielectric constant εr: 4,6 (1 MHz ; 25 °C)
  • Loss tangent (tan δ):
    37 x 10-4 (1 MHz ; 25 °C)
  • Logarithm of the electrical volume resistivity lgρ:
    • 8,0 Ω x cm (250 °C)
    • 6,5 Ω x cm (350 °C)

Standard Glass Thicknesses

(To place an inquiry click on the thickness)



48h- Express Service icon
0,70 ±0,05
0,70 ±0,07
1,10 ±0,05
1,10 ±0,10
1,75 ±0,20
2,00 ±0,05
2,25 ±0,20
2,75 ±0,10
2,75 ±0,20
3,30 ±0,20
3,80 ±0,20
5,00 ±0,20
5,50 ±0,20 -
6,50 ±0,20
7,50 ±0,30 -
8,00 ±0,30 -
9,00 ±0,30 -
11,0 ±0,30 -
13,0 ±0,50 -
15,0 ±0,50 -
16,0 ±0,50 -
17,0 ±0,50 -
18,0 ±0,50 -
19,0 ±0,50 -
21,0 ±0,70 -
25,4 ±1,00 -

The marked glass thicknesses () are available within our 48h–Express Service.

If you need additional information about SCHOTT BOROFLOAT® 33 glass or our manufacturing capabilities, please do not hesitate to contact us.


All given details and specifications are mean reference values and are not guaranteed. Also, please consider our "Notes on specifications".

© 1994-2019 Präzisions Glas & Optik GmbH