The important considerations to be taken into account in the development of test methods and in the preparation of Test Procedures are described in this Guide. Suggestions are included concerning aging temperatures, environmental conditioning, and the reporting of test results. The objective of the Test Procedures is to provide methods for determining the relative thermal life of insulating materials. The data obtained should provide the basis for establishing temperature classifications for materials. The thermal life values of the materials tested should provide preliminary data which can be used in selecting insulating materials for electric equipment. Test Procedures should also provide methods for determining the rate at which the important properties of materials deteriorate with thermal aging. To perform satisfactorily, insulating materials must have the required combination of physical, chemical, and dielectric properties. These properties should be evaluated separately by test methods not within the scope of these Test Procedures. These Test Procedures are intended to determine the changes in properties of materials caused by thermal aging.