A hydrophobic dielectric sealing material is provided that is especially suitable for use in extreme environments such as for enabling downhole electrical feedthrough integrated logging tools reliable operation, especially, in a water or water-mud filled wellbore as first scenario or in moisture-rich oil-mud filled wellbores. In some embodiments, a hydrophobic dielectric sealing material may include: H.sub.3BO.sub.3 10-60 mol %; Bi.sub.2O.sub.3 10-50 mol %; MO 10-50 mol %; SiO.sub.2 0-15 mol %; and optionally one or more rare earth oxides 0-5 mol %. A method for making hydrophobic sealing material includes selecting water insoluble raw materials, form tetragonal phase dominated phase, and enlarge band-gap with wide-band-gap material. The morphology of the sealing material is preferably a tetrahedral phase dominated covalent bond network for obtaining high electrical insulation resistance, dielectric strength and hydrophobicity, and high mechanical strength in against downhole 30,000 PSI/300 C. water-based hostile environments.