Silicones are widely used for electrical insulation due to their high dielectric strength and thermal stability. However, recent studies revealed insufficient stability of silicone at high temperature for aerospace application. In this study, effect of Al2O3 fibers on thermal stability of silicone was investigated by thermogravimetric analysis (TGA) and isothermal (250 degrees C) soak test. Both tests indicated an increased thermal stability with increasing fiber-loading. In TGA tests, temperature of degradation onset increased from 330 to 379 degrees C with a 30 wt% fiber-loading. In soak tests, pure and 30 wt%-filled silicones lost 10% of polymer weight in 700 and 1800 h, respectively. Improved thermal stability was explained by restrained chain mobility caused by interfacial hydrogen bonds, whose effect was then investigated by dehydrating Al2O3 fibers at high temperature in N-2 to partially destroy the bonds. Removal of hydrogen bonds impaired thermal stability, increasing the initial weight-loss rate from 0.025 to 0.036 wt%/hour. (C) 2014 Elsevier Ltd. All rights reserved.