The understanding of the failure mechanism causing cracks in insulated telephone wire is critical to developing a solution to the problem. This paper reviews the antioxidant and metal deactivator theory as it applies to polyolefins and reviews the factors, both internal to the polymer and external which affect stability. Degradation theory in vacuum and air is reviewed. Primary and secondary antioxidants are discussed as are multifunctional metal deactivator/antioxidant molecules. The internal factors affecting thermal stability which are discussed include : polymer synthesis process, molecular weight, molecular weight distribution, crystallinity, phase state, orientation, amount of antioxidant, amount of metal deactivator, and amount of blowing agent. The external factors affecting long term life are : temperature, oxygen, ozone, stress, filling compound, and presence of copper.