Optical Glass picture, Borofloat
Home / Products / Technical Glass / BOROFLOAT 33 Borosilicate Glass

BOROFLOAT® 33 Borosilicate Glass

Temperature- and chemically resistant glass

Special Properties

  • High temperature load capacity:
    - up to 450°C permanent load
    - up to 500°C temporarily (< 10h)
  • Low thermal coefficient of expansion
  • Thermal coefficient of expansion matches the one of
    silicon wafers (anodic bonding)
  • High thermal shock resistivity
  • Clear, practically colorless appearance
  • Low self-fluorescence
  • High UV-Transmission
  • High chemical resistivity against strong acids,
    bases and organic substances
  • Low alkali content in the glass composition
  • Low specific weight
  • Good scratch and abrasion resistance
  • High elasticity and mechanical strength
  • Superior flatness obtained by micro-float process

Typical Applications

  • Glass substrates for dielectric coatings
  • Lighting applications
  • Front window for high power floodlights
  • Substrates for optical filter coatings
  • Wafer substrates
  • Anodic bonding
  • Biotechnology
  • Photovoltaic glass
  • Sight glass windows
  • Environmental technology
  • Chemically resistant glass slides
  • Harsh environments
  • Neutron absorbers
  • Measurement and sensor technology
Borofloat window
nullspacer Fig.: CNC-manufactured, temperature resistant window made of BOROFLOAT® borosilicate glass. Parts like this optical window for a micro reactor can economically be made of borosilicate glass.

BOROFLOAT® glass offers a superior optical quality. Resulting from a special micro-float manufacturing process developed by SCHOTT, BOROFLOAT® features a good flatness, surface quality, a low micro roughness and a good homogeneity. BOROFLOAT® is a clear-transparent white borosilicate glass material. The glass has a low self-fluorescence over a broad light spectrum, which facilitates a wide scope of applications in the field of optics, optoelectronics, photonics and analytics.

BOROFLOAT® 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 of time and at temperatures higher than 100°C. BOROFLOAT® glass exceeds the chemical resistance of most metals and most other glass materials. Because acids and bases only dissolve marginal amounts of ions out of the glass, test results are not affected. This property opens up the possibility of interesting applications in the field of medical engineering and analytics. But also the mechanical characteristics of BOROFLOAT® surpass the ones of soda-lime float glass and that of most other borosilicate glass materials.

BOROFLOAT® flat glass is an ideal raw material for optical coatings, mirrors, filters, windows or glass wafers and has shown to be a good and economical choice for many different technical glass applications, particularly at high operating temperatures which cannot be resisted by soda lime glass. The borosilicate glass has an almost identical coefficient of thermal expansion and nearly the same specific weight as PYREX® sheet glass and is often used to replace this material which has been discontinued many years ago. BOROFLOAT® 33 is a registered trademark of SCHOTT AG.

To request windows or substrates or any other optics made of original SCHOTT BOROFLOAT® glass with individual dimensions, please use the button below:

Request for Quotation

48h- Express Service icon

48-h Express Service available

Note: Other borosilicate glass materials like MEMpax®, D263 T, SUPREMAX® or DURAN® from SCHOTT are also part of our extensive manufacturing and delivery program. For additional detailed information please contact us.


UV-VIS-IR Transmission

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

UV-VIS-IR transmission of BOROFLOAT® glass


UV-Transmission at 0,7mm thickness

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

UV-transmission of BOROFLOAT® at 0,7mm thickness


UV-Transmission at 3,3mm thickness

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

UV-transmission of BOROFLOAT® at 3,3mm thickness


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 of Borofloat glass


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 of Borofloat borosilicate glass:
    • 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 if the following RTG and RTS values
    are considered)
    • for short term load 500°C (< 10 h)
    • for long term load 450°C (≥ 10 h)
  • Resistance to thermal gradients (RTG):
    • 110K (< 1h)
    • 90K (1-100h)
    • 80K (> 100h)
      (Testing method description on request)
  • Resistance to thermal shock (RTS):
    • 175K (at thickness ≤ 3,8mm)
    • 160K (at thickness = 5,0-5,5mm)
    • 150K (at thickness = 6,5-15,0mm)
    • 125K (at thickness > 15,0mm)
      (Testing method description on request)

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 of Borofloat


Reaction time/

Weight loss

5 Vol.% HCl
24h at 95°C
0,02 n H2SO4
24h at 95°C
24h at 95°C
5% NaOH
6h at 95°C
0,02 n NaOH
6h at 95°C
0,02 n Na2CO3
6h at 95°C
10% HF
20min at 23°C
10% NH4F x HF
20min 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
(click thickness for a quote)



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

The thicknesses marked with X are available within 48-h Express Service

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