The results of a comprehensive study of the physical and mechanical characteristics of the mica-containing groundwall insulation of stator windings for high-voltage turbogenerators are presented. A comparative analysis was carried out for insulation manufactured using resin-rich (RR) and vacuum pressure impregnation (VPI) technologies. Strength and deformation characteristics under various types of mechanical loading were determined, interlayer adhesive strength was assessed and thermal expansion was evaluated, taking into account the material’s anisotropy. Significant differences in the behavior of the studied insulation types at elevated temperatures have been established. A significant anisotropy of the thermophysical properties of the material has been revealed. Accelerated thermal aging tests demonstrated the retention of mechanical characteristics over a long service life. The obtained results are of practical importance for calculating the thermomechanical and vibrational stability of the insulation systems of high-voltage turbogenerators.