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BOROFLOAT® 33 & Optical Mirrors: A Union of Inspiration & Quality

The performance requirements for optical mirrors are extremely rigorous as slight deviations can have significant impacts on the outcome of specific performance. Thermal stability is a must if mirrors are used in environments subjected to temperature changes. Excellent surface quality combined with exceptionally high transmission and reasonable cost are other attributes that engineers consider when specifying their material of choice. BOROFLOAT® glass meets such demanding requirements and has been used for sophisticated optics around the globe.
BOROFLOAT® 33 & Optical Mirrors: A Union of Inspiration & Quality

BOROFLOAT® - The sum of its properties is what makes it unique for optical mirrors!

  • Exceptionally high transparency
  • Outstanding thermal resistance
  • High chemical durability
  • Broad range of sizes and thicknesses

Optical mirrors made of BOROFLOAT® glass offer outstanding transmission

BOROFLOAT®´s exceptionally high transparency, outstanding visual quality and optical clarity make it the material of choice for many optical applications in research and industry. High transparency in visible and near IR & UV range of wavelengths offers customers a vast wealth of new possibilities. Specific light transmittance values are thickness dependent and significantly influenced by Fe2O3 impurity levels. BOROFLOAT® specialty glass uses only the purest raw materials resulting in extremely low (~90 ppm) iron impurity levels and hence exceptionally high transmission values. In fact BOROFLOAT® is the industrial glass with the lowest level of iron impurity of all float glass materials in the market.
Optical data
Abbe number
(ve = (ne – 1) / (nF‘ – nC‘))
Refraction index (nd587.6 nm)) 1.47140
Dispersion (nF – nC) 71.4 x 10-4
Stress-optical coefficient (K) 4.0 x 10-6 mm2 N-1

* According to ISO 7991.

BOROFLOAT® glass - the ideal substrate for applications that require low inherent fluorescence

Some materials have the ability to emit electromagnetic radiation after being activated by high energy radiation. This property is referred to as fluorescence. It depends on the material’s purity and structural characteristics as well as the radiation’s excitation energy and excitation wavelength. BOROFLOAT® 33 is a highly transparent glass with a much lower inherent fluorescence than soda-lime flat glass.

Optics made of BOROFLOAT® glass are resistant to thermal loads and chemical attacks

The glass composition of BOROFLOAT® specialty glass is not only tailored towards excellent optical properties. It is also designed to provide very low thermal expansion and high chemical durability. The element boron plays a significant role in delivering such special properties as it determines how strong the bonds are within the glass network. BOROFLOAT® glass is used whenever very good temperature stability and excellent resistance to thermal shock are required. It can be thermally toughened and thermally shaped (3D). BOROFLOAT® is also highly resistant to hydrolytics, acids and alkalis and is known for its low alkali diffusion.
Thermal properties
Coefficient of
Linear Thermal Expansion (C.T.E.) α (20 - 300 °C)
3.25 x 10-6 K-1 *
Specific heat capacity
cp (20 - 100 °C)
0.83 kJ/(kg·K)
Thermal conductivity λ (90 °C) 1.2 W/(m·K)

* According to ISO 7991.
Chemical durability
Hydrolytic resistance
(according to ISO 719 /
DIN 12 111)
(according to ISO 720)
 HGA 1
Acid resistance (according to ISO 1776 / DIN 12 116)  1
Alkali resistance (according to ISO 695 /
DIN 52 322)
A 2
Maximum operating temperatures
For short-term usage (< 10 h)
500 °C
For long-term usage (≥ 10 h) 450 °C
The maximum operation temperatures for BOROFLOAT® should be seen in conjunction with RTG (Resistance to Temperature Gradients) and RTS (Resistance to Thermal Shock) values. Such values and test methods are available on request.
Working Point (104 dPas)
1270 °C
LITTLETON temperature / Softening Point (107,6 dPas) 820 °C
Annealing Point (1013 dPas) 560 °C
Strain Point (1014,5 dPas) 518 °C
Transformation temperature (Tg) 525 °C

The right size and thickness for any application

Forms supplied

BOROFLOAT® 33 is available in the following standard thicknesses and tolerances:


BOROFLOAT® 33 is available in the following standard sizes:
Standard thicknesses
0.70 ± 0.05
1.10 ± 0.05
1.75 ± 0.05
2.00 ± 0.05
2.25 ± 0.05
2.75 ± 0.10
3.30 ± 0.20
3.80 ± 0.20
5.00 ± 0.20
5.50 ± 0.20
6.50 ± 0.20
7.50  ± 0.30
9.00  ± 0.30
11.00  ± 0.30
13.00   ± 0.30
15.00   ± 0.40
16.00  ± 0.50
19.00   ± 0.50
21.00 ± 0.70
25.40 ± 1.00

Panel thickness is continuously measured during production using laser thickness measuring equipment. Further thicknesses and tolerances are available on request.
Standard sizes
Size Thickness
1,150 x 850 mm 0.7 – 25.4 mm
1,700 x 1,300 mm 16.0 – 21.0 mm
2,300 x 1,700 mm 0.7 – 15.0 mm