Borofloat Glass

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 glass is often used as an less expensive equivalent to Pyrex for many applications. The materials differ in their chemical composition in the alkali ratio of Na2O to K2O and in their content of oxidic minor components which affects the transmission of the material. Consisting of natural raw materials, Borofloat is harmless to both humans and to the environment, and is also recyclable.

Available Sizes

Borofloat is a sheet glass which comes in many standard thicknesses ranging from .7mm, 1.1mm, 1.75mm and up, all the way to 21mm thick. Valley Design provides this material for wafers, substrates, and other components. Typical geometries range from 1" square or round, 2", 3", 4" (100mm), 5" (125mm), 6" (150mm), 8" (200mm) and 12" (300mm). If required, Valley can fabricate other dimensions, and also polish this material to custom thicknesses. For a quotation to meet your specifications, please e-mail your request or call 831.420.0595.

Principal Uses

Borofloat borosilicate glass wafers and borofloat substrates are used for precision engineering and optical applications, electric insulators, neutron absorbers in nuclear energy applications, vision and cover panels, linings in chemical industry equipment, slides for Biotechnology applications, filters, telescope mirrors, display glass and sensors for electronics, MEMS applications, anodic bonding, and silicon on insulator.

Thermal Properties

Thermal Coefficient of Expansion (20-300°C): 3.25 x 10^-6 K^-1
Specific Thermal Capacity (20-100°C): 0.83 KJ x (kg x K)^-1
Specific Thermal Conductivity (90°C): 1.2W x (m x K)^-1
Transformation Temperature Tg: 530°C/986°F
Annealing Point: 560°C/1040°F
Softening Point: 815°C/1508°F
Thermal Conductivity: 1.2 W/mK @90°C
Maximum Operating Temperature Considering RTG (Resistance to Thermal Gradients) and RTS (Resistance to Thermal Shock):
      Short Term: 500°C/932°F
      Long Term: 450°C/842°F

Mechanical Properties

Density (25°C/77°F): 2.23 g/cm³
Modulus of Elasticity: 63 kN/mm²
Young's Modulus (25°C/77°F): 64kN/mm²
Knoop Hardness HK 0.1/20: 480
Poisson's Ratio: 0.2
Bending Strength: 25 MPa

Optical Properties

Refractive Index: 1.471
Index of Refraction:
      @ 435.8nm = 1.48
      @ 589.3nm = 1.47
      @ 656.3 = 1.46
Dispersion: 71.4 x 10^-4
Abbe Constant: 65.41
Optical transmission

Chemical Properties

Hydrolytic Resistance: Class 1
Acid Resistance: Class 1
Alkali Resistance: Class 2

Material Composition

SiO₂: 81%
B₂O₃: 13%
Na₂O/K₂O: 4%
Al₂O₃: 2%

Electrical Properties

Dielectric Constant: 4.6 @1MHz & 25°C
Loss Tangent: 37 x 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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Updated: 10 January 2011

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