The coil insulation on most magnets for use with accelerators consists of inorganic materials such as glass fiber and fillers impregnated with organic compounds such as epoxies, polyesters, and silicones. Many of the usual combinations are damaged if subjected to high radiation levels such as those anticipated at the Stanford Linear Accelerator, where the expected dose rate may be as high as 1011 rads per year. This paper describes certain tests carried out at SLAC in which several commercially available insulations were found to deteriorate severely at total doses of as low as 1010 rads. Changes in molecular structure induced by radiation effects and degradation of electrical and mechanical properties are discussed. The development and testing of an insulation using pure AI2O3 fillers which have retained approximately 25% of its original mechanical strength at an absorbed radiation dose of 3.25 X 1012 rads will be described. This insulation requires minor changes in the usual winding and "potting" techniques prevalent in the industry. Interesting changes in the crystal structure of the filler are observed under irradiation.