Presented investigations are based on three fundamental relationships for materials: “modulus of elasticity-temperature”, “strength-temperature” i.e. the kinetic nature of solids strength, and nonlinear “stress-strain” dependency. It is shown that for polymers, concrete and polymer concrete insulators the dielectric and mechanical properties decrease with temperature. Preliminary results are promising for predicting dielectric strength and time to failure of insulators knowing their properties at room temperature.