Electro Glass Products now offers M3-289 glass as a Corning 7070 substitute. The M3-289 lithia potash borosilicate glass is specifically designed for high frequency electrical applications requiring 50-ohm impedance. This glass has a very low coefficient of thermal expansion making it more resistant to thermal shock compared to most other common glasses. It also has high electrical resistivity and thus a very low conductor of electrical current. These characteristics make the M3-289 glass ideal for RF and Microwave frequency feedthroughs, especially for those used in harsh environments.