Low-Expansion Borosilicate Glass (LEBG)

The most well-known low-expansion borEBG is typically less homogeneous and contains more striae and bubbles than optical glasses such as BK7. This material is ideally suited to such tasks as mirror substrates, condenser lenses for high-power illumination systemosilicate glass (LEBG) is Pyrex® made by Corning. It is well suited for applications in which high temperature, thermal shock, or resistance to chemical attack are primary considerations. On the other hand, Ls, or windows in high-temperature environments. Because of its low cost and excellent thermal stability, it is the standard material used in test plates and optical flats. As seen in the figure below, transmission of LEBG extends into the ultraviolet and well into the infrared.

Low-Expansion Borosilicate Glass Constants
Abbé Constant
Density (@ 25°C)
2.23 g/cm-3
Young's Modulus
5.98 x 109 dynes/mm2
Poisson's Ratio
Specific Heat at 25°C
0.17 cal/g-°C
Coefficient of Linear Expansion (0°C to 300°C)
3.25 x 10-6/°C
Softening Point
Melting Point
Pyrex® is a registered trademark of Corning, Inc.
External transmittance for 8-mm-thick uncoated low-expansion borosilicate glass