Abstract SAMPLES of rubber-insulated wire were aged by exposing to the diffused light in the physical testing laboratory. The thickness of wall of rubber surrounding the tinned copper wire showed a variation from 0.030 to 0.065 inch (0.76 to 1.65 mm.). The thickness of wall of rubber surrounding the tinned copper wire showed a variation from 0.030 to 0.065 inch (0.76 to 1.65 mm.). The samples were tested for tensile strength and elongation during the aging interval and the results were then compared with accelerated life tests obtained on the same samples when new. Average results on 480 different compounds, ranging in quality from a low-grade compound to a compound containing 60 per cent by weight of crude rubber, show the following relationship between shelf aging and accelerated aging.