1. A method of evaluating the sensitivity grade of an interior material used in vehicles comprising the steps of: (i) evaluating sensitivity properties of an interior material, wherein microfibers having a fineness of 0.001 to 0.3 denier are interlocked in a nonwoven, elastic polymers are impregnated therein, and the microfibers are standing on the surface to form fluffs, before irradiating the interior material with xenon arc to provide noise factors; (ii) irradiating the interior material with xenon arc having a wavelength in the range from 300 to 400 nm to provide noise factors, and after irradiating evaluating sensitivity properties of the interior material; (iii) averaging each of the sensitivity properties evaluated before the provision of noise factors and after the provision of noise factors to obtain the average value (safety factor) of each of the sensitivity properties; (iv) comparing the average value (safety factor) of each of the sensitivity properties with a predetermined target value of each of the sensitivity properties to compute a target value achievement level of each of the sensitivity properties; and (v) determining the sensitivity grade of the interior material based on the sensitivity property with the lowest target value achievement level.