An insulator for covering electric conductors is used to cover, for the purpose of providing insulation, lead wires of the coils in rotary electric machines or stationary induction motors or conductors for connecting various electrical machinery and apparatus. The insulator is comprised of a flexible plastic film tube provided with a soft material on its inner surface. Such a construction prevents the insulation from being damaged even if the electric conductor has corners or bends or even if an external force is applied to the electric conductor because the soft material is compressed and deformed to absorb the applied force.